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Class _S_5i3_L 
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CQESRIGHT DEPOSm 



Bgricultural Science Series 

L. H. BAILEY, Editor 



THE NATURE AND 
PROPERTIES OF SOILS 



AGRICULTURAL SCIENCE SERIES 

UNDER THE EDITOESHIP OF 

L. H. BAILEY 



THE NATURE AND PROPERTIES OF SOILS, 
by T. Lyttleton Lyon and Harry 0. Buclcman 



THE NATURE AND 
PROPERTIES OF SOILS 

A COLLEGE TEXT OF EDAPHOLOGY 



T. LYTTLETON LYON 

FEOFESSOB OF SOIL TECHNOLOGY, COENELL UNIVEESITT 



HARRY O. BUCKMAN 

PEOFESSOE OF SOIL TECHNOLOGY, COENELL UNIVEESITT 



THE MACMILLAN COMPANY 
1922 

All rights reserved 



FEINTED IN THE UNITED STATES OF AMERICA 






Copyright, 1922, 
By the MACMILLAN COMPANY. 



Set up and electrotyped. Published April, 1922. 



APR 19 1922 
0)C!.A659657 



TABLE OF CONTENTS 

CHAPTER PAGE 

I. Some Conceptions of the Soil and Its Relation to 

Plants 1 

II, Soil Forming Processes 16 

III. The Geological Classification of Soils 38 

IV. The Soil Particle and Certain Important Relations 66 
V. The Organic Matter op the Soil 99 

VI. The Colloidal Matter of the Soil 127 

VII. Soil Structure and Its Modification 139 

VIII. The Forms of Soil Water and Their Characteristics 151 

IX. The Water op the Soil in Its Relation to Plants . 184 

X. The Control of Soil Moisture 202 

XI. Soil Heat 223 

XII. Soil Air 247 

XIII. The Absorptive Properties of Soils 263 

XIV. The Soil Solution 275 

XV. The Removal op Nutrients from the Soil by Cropping 

AND Leaching 289 

XVI. Chemical Analysis op Soils 311 

XVII. Alkali Soils 328 

XVIII. Soil Acidity 345 

XIX. Liming the Soil 362 

XX. Soil Organisms, Carbon, Sulfur and Mineral Cycles 384 

XXI. Soil Organisms — the Nitrogen Cycle 409 

XXII. Commercial Fertilizer Materials 442 

XXIII. The Principles of Fertilizer Practice 471 

XXIV. Farm Manure 499 

XXV. Green Manure 535 

XXVI. The Maintenance of Soil Fertility 552 

Index op Authors 561 

Index op Subject Matter 567 

V 



NATURE AND PROPERTIES 
OF SOILS 



CHAPTER I 

SOME CONCEPTIONS OF THE SOIL AND ITS RELA- 
TIONS TO PLANTS 

Due to the action of climatic agencies the outer solid por- 
tions of the earth readily pass into a loose and disintegrated 
condition. This layer, although superficial and insignifi- 
cant in comparison to the bulk of the earth, has performed 
and is still performing a marvelous function. Life on the 
earth has been slowly but steadily developing and changing 
until we see about us the forms that characterize our age. 
This evolution has depended to no small degree on this super- 
ficial layer of decomposed rock with its admixture of de- 
caying organic matter which together form the soil. In 
this medium many and varied organisms have lived and from 
it have drawn, wholly or in part, their sustenance, leaving 
as a recompense a contribution of organic debris, which in its 
turn has given rise to reactions of almost unbelievable com- 
plexity. 

Like the life which it has sustained and nourished, the 
soil has been changing and evolving. The soil of today 
is not the soil of yesterday nor will it be the soil of tomorrow. 
It is never still. It is continually seeking a mechanical and 
chemical adjustment with the forces which surround it or 

1 



2 NATURE AND PROPERTIES OF SOILS 

are active within its precincts. Such an equilibrium it never 
attains and thus the evolution goes on and on. It is this 
continual change and this endless response to environment 
that makes the soil useful to plants. The disintegrating 
rock and the decaying organic additions are thus converted 
into a mechanical support for plants, while at the same 
time they are forced to liberate the nutrients essential to 
plant growth. 

In the light of its origin and function the soil may be 
defined as a mixture of broken and weathered fragments of 
rock and decaying organic matter, which covers the earth 
in a thin layer and supplies mechanical support and in part 
sustenance to plants. 

This debris of rock and plant residue, teeming with its 
microscopic life and ever restless in its endless efforts at 
equilibrium, is the arable soil from which man must obtain 
his bread. As the light of investigation is thrown on it, 
new changes, new functions and new and unsuspected re- 
lationships are brought to view until the story of the soil 
may be retold with a clearer insight into those processes 
that render it useful to man. 

1. Composition of the soil. — The soil as defined is com- 
posed of two general classes of material, mineral and organic. 
The former in most cases makes up from 90 to 99 per 
cent, by weight of the dry substance of a soil, the organic 
matter, except in the case of peat and muck, being in rela- 
tively smaller amounts. In spite of the low proportion of 
organic matter its presence is vital, not only because of its 
influence physically but because of the nutrients, especially 
nitrogen, that it carries. The mineral portion of a soil 
functions as a frame-work and as a source of certain chem- 
ical elements, which are necessary to proper crop growth and 
development. 

It must be realized at the very outset that the two main 
constituents in a normal soil exist in very intimate relation- 



SOME CONCEPTIONS OF THE SOIL 



ship, reactions occurring not only within each group but 
between the groups as well. Unless such interactions take 
place it is unlikely that the mixture will ever be in a con- 
dition either chemically, physically or biologically to sus- 
tain plant growth. These reactions, although very complex, 
take place with surprising ease and rapidity. As a con- 
sequence the study of this complex, heterogeneous and 
highly dynamic mass that 
we call the soil is often be- 
set with difficulties that 
completely baffle our pres- 
ent facilities for its study. 
2. Soil-forming rocks.' 
— In any study of soil 
origin or composition, how- 
ever cursory, the geological 
phases of the problem im- 
mediately force attention. 
This is due to the bearing 
that certain geological phe- 
nomena have on soil condi- 
tions and crop growth. In 
the soil we find that the 
inorganic materials have 
originated from the com- 
mon rocks. The best known 
country rocks are of course 
involved because they present the greatest outcrop surface and 
of necessity must contribute most to the mineral fabrication of 
the soil. They are classified under three heads — igneous, sedi- 
mentary and metamorphic. The most important types from 
the standpoint of soil formation are the following : 

* For excellent nontechnical discussions of rocks and minerals: — 
Pirsson, L. V., Eocks and Eock Minerals; New York, 1915. Merrill, 
G. P., Eocks, Eock Weathering and Soils; New York, 1906. 




ORGANIC- 
10% 

Fig. 1. — Volume composition of a 
loam soil when in good condition 
for plant growth. The air and 
water in a soil are variable and 
their proportion determines to a 
considerable degree the productiv- 
ity. 



4 NATURE AND PROPERTIES OF SOILS 

Igneous Sedimentary Metamorphic 

Granite Limestone Marble 

Syenite Dolomite Schist 

Diorite Shale Slate 

Gabbro Sandstone Quartzite 

Basalt Conglomerate Gneiss 

The mineralogical complexity of rocks has an important 
bearing on the question of soil formation and soil composi- 
tion. The fragments of any soil are, for the most part, dis- 
tinguishable as separate minerals rather than as mineral aggre- 
gates. For example, a soil from a granite would be char- 
acterized by separate grains of quartz, orthoclase, micro- 
cline and perhaps mica rather than by fragments of the orig- 
inal granite itself. Again, it is the composition of the easily 
decomposable minerals rather than the composition of the 
bulk rock that determines what simplifications shall occur, 
what new substances shall arise in the soil and what elements 
shall be liberated for plant use. 

3. Soil minerals. — Although hundreds of minerals have 
been identified, comparatively few are common or important ^ 
in rock formation. As a consequence, the list of im- 
portant minerals found in soils will be correspondingly cur- 
tailed, although enough are always present, especially in the 
finer portions, to make the soil very complex mineralogically. 
The minerals as to origin may be divided into two groups: 
(1) those that persist from the original rock and (2) those 
that are produced by the decomposition of the original min- 
erals, during soil formation. For example, the quartz grains 

' The following table indicates the approximate proportions of the 
common minerals in the earth's crush to a depth of ten miles: 

Feldspars 57.8% Clay 1,0% 

Amphibole and Py- Carbonates 5 

roxene 16.0 Limonite 2 

Quartz 12.7 All others 8.2 

Mica 3.6 

Kecalculatcd from Clarke, F. W., Data of Geochemistry ; U. S. Geol. 
Survey, Bui. 695, pp. 32-33. 1920. 



SOME CONCEPTIONS OF THE SOIL 



of soil almost always come directly from the original rock 
as do particles of orthoclase, biotite, and apatite. Hematite, 
the kaolinite group and the chlorite and epidote groups 
generally originate in soils through weathering. The fol- 
lowing list of minerals is by no means complete, yet it includes 
the more important forms from the soil and plant standpoint. 

A LIST OF THE MOST IMPORTANT SOIL MINERALS.* 
(The elements in bold type are those necessary for plant nutrition.) 



1. Quartz 

2. Orthoclase and 
Microcline feldspar 

3. Muscovite mica 

4. Biotite mica 

5. Plagioclase feldspar 

6. Calcite and Dolomite 

7. Hornblende and Augite 

8. Olivine 

9. Apatite 

10. Kaolinite group 

11. Serpentine and Talc 

12. Chlorite group 

13. Epidote group 

14. Hematite 

15. Limonite group 



SiOs 
KAlSiaOs 

KH^AlgSigOio 
KHMgFeAl/sigOia 
Ca and Na aluminum silicates 
CaCO,, and (Ca, Mg) CO3 
Ca, Mg, Fe aluminum silicates 
(Mg, Fe),SiO, 
Ca^ (P0J3(C1, F) 
Typified by kaolinite. 

H.Al^Si^Og 
Hydrated Mg silicates 
Hydrated Mg, Fe aluminum 

silicates 
Hydrated Ca, Fe aluminum 

silicates 
Fe^Og 
Typified by limonite 2 FCoOg. 

3 H.O 



* Below are some of the most important mineralogical investigations of 
soil: McCaughey, W. G., and Williams, H. F., The Microscopic De- 
termination of Soil-Forming Minerals; U. S. Dept. Agr., Bur. Soils, Bui. 
91. 1913. Plummer, J. K., Petrography of Some North Carolina 
Soils and Its Relationship to their Fertilizer Requirements, Jour. Agr. 
Res., Vol. V, No. 13, pp. 569-581. 1915. Robinson, W. O., The Inor- 
ganic Composition of Some Important American Soils; U. S. Dept. Agr., 
Bui. 122. Aug., 1914. 



6 NATURE AND PROPERTIES OF SOILS 

4. Importance of soil minerals. — Quartz is found in al- 
most all soils, making up often from 80 to 90 per cent, of 
the composition, although a range from 40 to 70 per cent, 
is more common. Its universal presence is due to its hard- 
ness and insolubility. Quartz is a make-weight material, 
however, as it probably contributes but little to plant nutri- 
tion. In the form of sand, quartz has a great influence on 
the friability of soil, improving and maintaining the phys- 
ical condition to a marked degree. 

Orthoclase, microcline, muscovite and, to a lesser degree, 
biotite are important because of their potash content.^ They 
decompose, often rather readily, into kaolinite and similar 
products, thus liberating potassium in soluble form. The 
plagioclase feldspars also give rise to kaolinite. They carry, 
however, sodium and calcium. The latter element^ plays an 
important role in soil both as a nutrient and as an amend- 
ment. When not sufficiently active it must be applied in 
some form. Calcite and dolomite also carry calcium. Horn- 
blende and augite bear calcium as well as magnesium and 
iron. Olivine is a magnesium and iron silicate. The oxida- 
tion of the iron of the above minerals gives rise to hematite, 
so common as a red coloring matter of soil. 

Practically all of the phosphorus of the soil, either organic 
or inorganic, has its origin in apatite, yet this mineral occurs 
but sparingly either in rock or soil. It makes up but 6 per 
cent, of igneous rocks. This accounts for the small percent- 
age of phosphoric acid in most soils and explains why it is 
often added in fertilizers.^ 

*PIummer, J. K., Availahility of Potash in Some Common Soil- 
forming Minerals, Jour. Agr. Res., Vol. XIV, No. 8, pp. 297-315. 
Aug., 1918. de Turk, E., Potassium-hearing Minerals as a Source of 
Potassium for Plant Growth; Soil Sci., Vol. 8, No. 4, pp. 269-301. 1919. 

^Shorey, E. C. et al., Calcium Com,pounds in Soils; Jour. Agr. Res., 
Vol. VII, No. 3, pp. 57-77. Jan., 1917. 

^ Fry, W. H., Condition of Phosphoric Acid Insoluble in Hydro- 
chloric Acid; Jour. Ind. and Eng. Chem., Vol. V, No. 8, pp. 664- 
665. 1913. 



SOME CONCEPTIONS OF THE SOIL 7 

The members of the kaolinite group are decomposition prod- 
ucts resulting from the decay of the feldspars and similar 
minerals. While kaolinite itself shows no nutrients in its 
formula, it often carries considerable calcium, potassium, 
magnesium and phosphorus by absorption. Moreover, its 
close association with other decomposition products such as 
serpentine, talc, chlorite and epidote tends to accentuate its 
importance in plant nutrition. The plasticity and cohesion 
imparted to a soil by the presence of the kaolinite group 
and its associated minerals are of great practical importance 
as is also the capacity to hold, either physically or chemically, 
the bases already mentioned. 

Hematite and limonite are simple iron compounds and 
usually occur in the soil as a result of the decomposition of 
certain iron-bearing minerals such as biotite, hornblende and 
augite. These iron compounds impart the red and yellow 
colors so characteristic of certain southern soils. Most of the 
soluble iron of the soil has its source in these minerals. Hema- 
tite and limonite are produced by the same general processes 
as are the kaolinite group and are found in very intimate 
contact with the serpentine, epidote, chlorite and kaolinite. 

5. Soil organic matter. — One of the essential differences 
between a normal fertile soil and a mass of rock fragments 
lies in the organic content of the former. The organic matter 
practically all comes from plants and animals that have in- 
vested the surface of the soil and the soil material. Through 
the agency of bacteria and other organisms with which the 
soil is liberally supplied, this organic tissue quickly loses its 
original form, and becomes the dark incoherent material so 
noticeable in fertile soils. The decay is not one of immediate 
simplification, as might be supposed. The split-off compounds 
react not only with materials of a similar origin but also 
with the decomposing mineral fragments. This tendency pro- 
vides the intimate relationship between the organic and in- 
organic constituents of the soil already emphasized as an ex- 



8 NATURE AND PROPERTIES OF SOILS 

ceedingly desirable condition. Incidentally the soil is ren- 
dered thereby very much more difficult to study, especially 
chemically. 

The incorporation of organic matter in any soil, either by 
natural or artificial means, tends, if the proper decay occurs, 
to make the soil more friable. The water capacity is markedly 
increased and the vigor of the bacterial and chemical activ- 
ities stimulated to a marked degree. As these two latter 
actions progress, some of the organic matter passes into simple 
combinations, allowing certain elements to become available 
to crops. Nitrogen, which is held in the soil largely in organic 
combination, emerges in the form of ammonia, nitrites and 
nitrates. It is from a salt of nitric acid that most plants 
absorb their nitrogen. Small amounts of sulfur, phosphorus, 
potassium and calcium are liberated from the tissue as decay 
proceeds. The largest product of organic decay, however, is 
carbon dioxide (CO2), which in the soil becomes important 
as a solvent for minerals, thus hastening the decomposition 
processes. 

6. Factors for plant growth. — The growth and develop- 
ment of a plant depends on two sets of factors, the internal 
and external. The latter may be classified as follows: (1) 
mechanical support, (2) heat, (3) light, (4) oxygen, (5) 
water, and (6) nutrients.^ With the exception of light, the 
soil supplies, either wholly or in part, all of these conditions. 
Mechanical support is a function entirely of the soil. The 
comparatively loose and friable condition presented by most 
soils allows ample foothold to the ramifying roots. 

Air and water are easily supplied because of the open 
condition of the soil, and its large pore spaces. Temperature 
depends almost wholly on climatic relationships. The water 

^ Nutrients are materials from which food may be elaborated once 
they have been absorbed by plants. The energy for this synthetic proc- 
ess comes from the sun. A food is any substance from which the plant 
may obtain energy for its normal processes. A large proportion of the 
materials absorbed by plants are nutrients. 



SOME CONCEPTIONS OF THE SOIL 9 

of the soil acts as a plant nutrient in itself and functions 
also as a solvent for other materials. By its circulation it 
not only promotes solution but it continually brings nutrient 
elements in contact with the absorbing surfaces of the roots. 
The two prime functions of the soil are thus realized through 
the factors discussed above — mechanical support and a suffi- 
cient supply of certain nutrient elements under favorable 
conditions. 

7. Nutrient elements.^ — Although the physical condition 
of the soil exerts a far-reaching influence on plant growth, 
the relationships involved are more readily understood than 
those which have to do with plant nutrition. Moreover, the 
solubility of the necessary nutrients is very closely related 
to the complex processes of soil formation. Ten elements^ 
are usually considered as necessary for plant growth. If one 
is lacking, normal development will not occur. They may 
be classified as follows: 

From air or water From the soil 

Carbon Nitrogen Calcium 

Oxygen Phosphorus Magnesium 

Hydrogen Potassium Sulfur 

Nitrogen Iron 

Plants obtain most of their carbon and oxygen directly 
from the air by photosynthesis and respiration. The hydro- 
gen comes, at least partially, from water. All of the other 
elements, except a small amount of nitrogen utilized directly 
from the air by certain plants, are obtained from the soil. 
It must not be inferred, however, that the bulk of the plant 

^ For an excellent discussion of the functions of plant nutrients, see 
Kussell, E. J., Soil Conditions and Plant Growth, Chap. II, pp. 30-46; 
New York. 1915. 

* It may be possible that manganese and silicon and possibly chlorine 
and fluorine function as nutrients. They as well as sodium, aluminum, 
titanium, barium, strontium, and certain rarer elements are found in 
plant ash. 



10 NATURE AND PROPERTIES OF SOILS 

tissue is fabricated from the soil. Quite the reverse is true. 
Fresh plant tissue generally carries only from .5 to 2.5 per 
cent, of mineral material. In spite of this, it is the mineral 
elements of nutrition that generally limit crop growth since 
a plant can always obtain, except in cases of drought or 
disease, unlimited amounts of carbon, hydrogen and oxygen. 

8. Primary nutrient elements. — While all of the seven 
soil nutrients must be available that plants may grow normally, 
only four or five are likely to become limiting factors. The 
others are almost always in great sufficiency. These few, 
nitrogen, phosphorus, potassium, calcium and occasionally 
sulfur, receive as a consequence especial attention. They 
may limit growth because they are actually lacking or be- 
cause their availability is low. These conditions often occur 
in the same soil. 

Combined nitrogen exists in the soil to a large degree as 
a part of the partially decayed organic matter present 
therein.^ As decay proceeds, small quantities of this nitrogen 
appear as ammonia in combination with some acid radical 
such as the chloride or sulfate or with the hydroxal group. 
Later, it is changed through further bacterial action to the 
nitrate form, united with some bases such as calcium or po- 
tassium. It is from this latter combination that most plants 
obtain the greater part of their nitrogen. These inorganic 
nitrogen compounds, present at any one time in a soil, are 
but a small proportion of the total soil nitrogen. The air 
both above the soil and that circulating within its pores has 
been the original source of all the combined nitrogen. Nat- 
ural processes have facilitated the combination which has been 
necessary for such a transfer. The encouragement of such 

^ Certain rocks, particularly those of a sedimentary nature, carry 
considerable nitrogen. When such rocks weather, this nitrogen tends 
to become available. The organic matter, therefore, does not absolutely 
control the amount of nitrogen in a soil. Hall, A. D., and Miller, 
N. H. J., The Nitrogen Compounds of the Fundamental Bocks; Jour. 
Agri. Sci., Vol. II, Part 4, pp. 343-345. July, 1908. 



SOME CONCEPTIONS OF THE SOIL 11 

fixation processes, especially those of a biological nature, is 
a feature of practical soil improvement. 

Phosphorus has its origin in the mineral apatite (Cag- 
(P04)3(C1,F)) and exists in the soil not only in this form 
but as tri-calcium phosphate (Ca3(P04)2), iron and alum- 
inum phosphates (FeP04 and AIPO4) and in certain other 
inorganic complexes. It also exists in organic combinations 
of a constantly varying nature. It probably is utilized by the 
plant as a simple phosphate such as the mono- or di-calcium 
salt (CaH^CPO^), and Ca.JlAl^O,)^^. 

Potassium, as already stated, occurs in the soil in orthoclase 
and microcline (KAlSigOg), in mica, especially muscovite 
(HjKAlaSigOia), and in other aluminum silicates, both hy- 
drated and non-hydrated. These complex forms supply potash 
to the soil solution and thus to the plant at a more or less 
rapid rate in the bicarbonate, carbonate, chloride, nitrate, and 
sulfate forms. 

Calcium, while necessary in the soil as a nutrient, also 
functions as an amendment in that it seems to preserve a 
proper soil reaction. It is possible that this relationship is as 
much nutritive as strictly chemical. Calcium exists in the soil 
in many minerals, of which calcite, plagioclase feldspar, horn- 
blende and augite are perhaps the most important. It is 
carried as an absorbed compound by kaolinite and similar 
materials. Calcium becomes available in the soil as the ni- 
trate, bicarbonate, chloride, phosphate, and sulfate. 

Sulfur is found in the soil in rather small amounts and 
generally forms a part of the organic matter. Inorganically 
it usually occurs as a sulfate combined with the common 
bases. In this form it is available to plants. The original 
source^ of most of the soil sulfur has been pyrite (FeSg), the 

' Considerable sulfur is brought to the soil in atmospheric precipita- 
tion. From 5 to 150 pounds an acre a year have been reported. Wilson, 
B. D. Sulfur Supplied to the Soil in Eain Water, Jour. Amer. Soe, 
Agron., Vol. 13, No. 5, pp. 226-229. 1921. 



12 



NATURE AND PROPERTIES OF SOILS 



commonest sulfide of this element. Although sulfur is no 
more abundant in the average soil than phosphorus, it is 
generally not considered as an extremely important fertilizing 
constituent. 

It is interesting to note at this point the amounts of the 
above elements in ordinary mineral soils. Generally the nitro- 



% 



5% 10% \^% 



80.11 



SiOs 

rc^Oj+AlgOj— 9.01 

HazO 2.0 ■ 

K2O 1.5 ■ 

CaO .61 



MgO- 
P205- 
SO5- 
N — 



-.51 
-.11 
-.11 



ORGAN IC- 



FiG. 2. — Chemical composition of a representative productive soil. 



gen (N) may range from .1 to .2 per cent., the phosphoric 
acid (expressed as PgOg) from .05 to .30 per cent, and the 
potash (expressed as KgO) from 0.5 to 2.0 per cent. Of the 
plant nutrients in the soil nitrogen, although usually present 
in small quantities, is relatively more available than is 
phosphoric acid or even potash. Phosphoric acid may be in 
the minimum because of its unavailability as well as because 
of the small quantity. Potash is commonly present in rela- 



SOME CONCEPTIONS OF THE SOIL 13 

tively large amounts. Its occurrence in complex and insoluble 
silicates makes its availability of vital consideration. The 
presence of abundant organic matter may have much to do 
with the liberation of sufficient potash for vigorous plant 
growth. 

The amount of lime (expressed as CaO) in soils is difficult 
to state with any degree of satisfaction because of a very 
wide range in composition. Some soils carry only a fraction 
of a per cent., while others, especially those formed under 
conditions where an originally high calcium content has been 
maintained or where calcium has accumulated, show as much 
as 10 or 12 per cent. The variability of the sulfur is much 
less. A range from .02 to .30 per cent, of sulfur (expressed 
as SO3) will include most soils. 

It is interesting at this point to note the average composi- 
tion of thirty-five representative American surface soils^, 
which were studied by the United States Bureau of Soils dur- 
ing a systematic investigation of the arable lands of the United 
States east of the Rocky Mountains. A comparison of these 
data with those setting forth the composition of the litho- 
sphere ^ may be made with profit. (Table I, page 14.) 

It is immediately noticeable that silicon, aluminum, and 
iron make up the greater portion of both soil and lithosphere 
and that the nitrogen, sulfur and phosphorus are particu- 
larly low in both cases. Magnesium, calcium, sodium, and 
potassium occur in fair amounts, especially in the earth's 
crust. It is noticeable also that the soil is much higher than 
the lithosphere in silicon, nitrogen, organic matter, and car- 
bon but much lower in all of the other constituents. These 
differences have developed as a result of the losses and gains 
during soil formation. 

^Robinson, W. O. et al., Variations in the Chemical Composition of 
Soils; U. S. Dept. Agr., Bui. 551. June, 1917. 

* The Lithosphere refers to the solid portion of the earth, in this case 
to a depth of ten miles. Clarke, F. W., Data of Geochemistry ; U. S. 
Geol. Survey Bui. 695, p. 33. 1920. 



14 NATURE AND PROPERTIES OF SOILS 

Table I 

Comparison of the Chemical Composition of American 
Surface Soils with that of the Lithosphere. 





35 American 


Composition of 


Constituents ^ 


Surface Soils 


lithosphere 


SiO^ 


84.67 


59.77 


AI3O3 


6.73 


14.89 


TiO^ 


.66 


.77 


Fe^Os 


2.53 


6.25 


MnO 


.06 


.09 


Na,0 


.49 


3.25 


K26 


1.03 


2.98 


CaO 


.40 


4.86 


MgO 


.27 


3.74 


P2O3 


.09 


.28 


SO3 


.09 


.28 


Nitrogen 


.07 a 


— 


Organic Matter 


2.61b 


— 


Carbon 


1.51c 


.03 



(a) Average of 22 soils only, (b) Average of 13 soils only, 
(c) Calculated from the organic matter. 

9. The soil and the plant. — As the soil considered agri- 
culturally is essentially a medium for crop production, its 
rational study has to do with the consideration and applica- 
tion of such scientific principles as have a bearing on prac- 
tical soil management. Anything that makes clearer the 
relationships between soil and crop has a proper place. Un- 
less a scientific phase has a crop relation, either directly or 
indirectly, it need receive but scant consideration. The com- 
position of the soil, its chemical and biological changes, its 
physical peculiarities and its reaction to certain additions 
must receive especial attention. More knowledge of the soil 

^ Soils contain many other elements, although in small amounts, such 
as chlorine, barium, csesium, chromium, lithium, molybdium, rubidium, 
vanadium, etc. Robinson, W. O., The Inorganic Constituents of Some 
Important American Soils; U. S. Dept. Agr., Bui. 122. Aug., 1914. 



SOME CONCEPTIONS OP TPIE SOIL 15 

will mean better systems of management and will allow the 
farmer to fulfill to a greater degree his duty to himself and 
to the State — the production of paying crops and the passing 
on to the next generation of a soil depleted as little as possible 
in fertility. 



CHAPTER II 
SOIL-FORMING PROCESSES 

The forces which have to do with soil formation are largely 
climatic in nature. They promote the physical and chemical 
breaking down of rock masses, they intermix there with the 
decaying organic matter and they shift the products from 
place to place. Even after the soil is apparently at rest and 
has become an effective agency in plant production, these 
same forces are still much in evidence. The physical and 
chemical evolutions through which mineral and organic mate- 
rials at or near the earth's surface are passing due to natural 
forces are spoken of as weathering} Erosion and deposition 
are terms referring to the natural translocations which soils 
and soil materials are frequently forced to undergo. 

If a soil represents a condition more stable than the rock, 
the rock change is in that direction. If a soil presents con- 
stituents or conditions not wholly stable to the forces effective 
at that particular time, it in turn seeks a change by an altera- 
tion or an elimination. A cycle of development is thus set 
up proceeding from youth to adolescence and even into old 
age. According to conditions, soils may age rapidly or slowly. 
Rejuvenation may even occur, while cases of arrested develop- 
ment may exist for short periods. 

10. Soil-forming processes classified. — While weather- 
ing, with the changes in form and composition which inva- 
riably accompany it, profoundly affects topography, it is very 

* The term weathering is somewhat misleading since it comprehends 
forces other than those generally considered as weather. All of the 
forces involved, however, depend upon climatic conditions. 

16 



SOIL-FORMING PROCESSES 17 

superficial in comparison to the earth's bulk. Nevertheless, 
the weathered mantle, in spite of its comparative insignifi- 
cance, presents an effective medium for plant growth. The 
agencies of formation, therefore, demand more than the brief 
mention just given. These forces are geologic when the soil 
is being evolved, but once the soil materials are in place, the 
actions become localized and the influences may be considered 
as soil processes rather than more broadly geological. 

The soil-forming processes^, while diverse both in action 
and product, may be classified under two heads, mechanical 
and chemical. The former is often designated as disintegra- 
tion, the latter as decomposition. • 

SOIL-FORMING PROCESSES 

I. Mechanical (disintegration) 

A. Erosion and deposition. 

Water, ice and wind.^ 

B. Temperature change. 

Differential expansion of minerals, exfoliation 
and frost. 

C. Biological influences. 

Plants and animals. 
II. Chemical (decomposition) 

A. Oxidation and deoxidation. 

B. Carbonation and decarbonation. 

C. Hydration and dehydration. 

D. Solution. 

11. The mechanical action of water. — From the time that 
that water as rain beats down upon the solid earth until it 
is finally discharged into the ocean, there to pound as waves 
upon the bordering lands, it is moving, sorting, and rework- 
ing the products of weathering. Water to erode must be 

' For a complete and detailed discussion of soil formation, see Merrill, 
G. P., Bocl'S, Eoclc Weathering and Soils; New York. 1906. Also, 
Emerson, H. L., Agricultural Geology; New York. 1920. 

^ Gravity is generally included in this group. While indirectly of 
great significance in soil formation, its direct action is not of great 
importance and is adequately disposed of in paragraph 27. 



18 NATURE AND PROPERTIES OF SOILS 

armed. Its cutting power, therefore, depends on the amount 
of sediment that it carries and on its velocity of flow. 
Erosion by water deserves particular attention, as its denud- 
ing effects are very rapid when geologically viewed. Most 
of the changes in topography are due to such activity. The 
material swept away is partly in suspension and partly in 
solution.^ The Appalachian Mountains, whose uplift was 
complete in Carboniferous times, have lost vastly more of their 
mass than now remains in view. 

While most of the debris from the ancient erosive cycles 
has been changed to rock or has become a noticeable charac- 
teristic of ocean water, remnants persist. To these remnants 
rivers, lakes and oceans are making, year by year, substantial 
additions. The cutting, carrying and depositing activity of 
streams produce alluvial soils of which the Mississippi flood 
plain is a well known example. Deltas built into oceans, lakes 
and gulfs represent stream activity under different condi- 
tions, while uplifted continental shelves are often bedded with 
erosive products. The delta and marine soils of the Atlantic 
and Gulf coastal plains afford examples of the latter types 
of soil production. Even the pounding, grinding and sorting 
activities of waves in ocean and lake are no mean factors in 
the mechanics of soil formation. 

12. Glacial action. — Ice at the present time, especially 
in temperate regions, is of little importance in soil forma- 
tion. Nevertheless, at a comparatively recent date geolog- 
ically, it had much to do with the preparation and deposition 
of soil materials over great areas in central and northern 
North America, northern Europe and the British Isles. Dur- 
ing the Great Ice Age immense continental glaciers succes- 
sively invaded these regions, much as the ice cap is over- 

* The chemical denudation by streams is generally spoken of as corro- 
sion. Abrasion is applied to the wear of the stream load upon its 
channel and of the particules in suspension upon themselves. Erosion 
is a broader term including corrosion and abrasion as well as trans- 
portation. 



SOIL-FORMING PROCESSES 19 

riding Greenland to-day. Of great thickness and weight and 
impelled southward by tremendous pressure, these ice sheets 
swept away the old soil mantle and ground the underlying 
rocks with irresistible energy. The heterogeneous debris, im- 
bedded in the ice, only served to enhance the cutting power 
of the slowly moving mass. Hundreds of square miles were 
covered and as the ice was often several thousand feet thick, 
mountains as well as hills were over-ridden. (See Fig. 3.) 

In the melting back of these tremendous ice sheets, the 
accumulated debris was of necessity left behind. When the 
ice retreat was rapid, the deposit was comparatively thin and 
uniform. When a halt occurred, the material was left in 
irregular hummocks. It is hardly necessary to state that the 
soil developed from the former deposit is the more important 
agriculturally, due to its level topography and wide extent. 
The area of the latter is fortunately small. The streams 
flowing from the ice fronts were no insignificant feature of 
the glacial phenomena. Such streams were heavily laden with 
sediment, which was distributed far and wide in regions miles 
beyond the ice front. 

In whatever manner the glacial debris was laid down it is 
necessary to note that such deposits were soil material, not 
soil. Chemical action in all its complexity and the interven- 
tion of plants and animals, especially the former, were neces- 
sary before a true soil could be born, a soil still in its youth 
and covering in the United States alone over 500,000 square 
miles. (See Fig. 3, page 20.) 

13. The influence of wind. — AVind, like water and ice, 
has both cutting and carrying power. The fluting of rocks, 
the polishing of stones, and the undermining of cliffs are of 
such frequent note as to require but brief mention. There 
seems no escape from the conclusion that wind is engaged in 
rock disintegration. Its geological function in arid regions 
seems similar to that of running water in humid lands. 

It is, however, as a transporting agency of fine materials 



NATURE AND PROPERTIES OF SOILS 







^^^lO' 



Fig. 3. — Sketch map of North America showing the approximate south- 
ward extension of the great ice sheets and the three centers of 
accumulation. 



SOIL-FORMING PROCESSES ^1 

that the wind is of especial importance in soil formation. The 
movement of sand and dust in both humid and arid regions 
is almost incessant. In desert storms 200 tons of materials 
liave been known to float over every acre of land. The finer 
particles travel for miles in a very short time. Southern Italy 
has received as much as one inch of dust from Africa during 
a single storm. The movement of sand dunes is but another 
evidence of the transporting power of air in motion. 

Wind as an agency in soil formation would perhaps receive 
much less attention were it not for the existence of large 
areas of a certain silty soil called loess. This soil exists along 
the Rhine both in France and Germany, in southern Russia, 
in Roumania, in China and in central United States. This 
material, as well as the adobe of our arid Southwest is con- 
sidered as largely wind laid. Since the loess is highly fertile 
and of great agricultural importance, added attention is thus 
directed towards wind as a soil-forming agency. (See Fig. 4.) 

14. Change in temperature. — Variations of temperature, 
especially if sudden or wude, greatly augment the denuding 
actions of water, ice, and wind. Rocks and soil become heated 
during the day and at night often cool much below the tem- 
perature of the air. This warming and cooling is particularly 
effective as a disintegrating agent. Rocks are mineral aggre- 
gates, the minerals varying in their coefficients of expansion. 
With every temperature change differential stresses are set 
n\), which eventually must produce cracks and rifts, since the 
minerals never assume their original position. Incipient focii 
for further physical and chemical change are thus established. 
Although the expansion coefficient of rock is low, it must be 
remembered that very large surfaces are involved. Moreover, 
it is the multiplicity of the rifts rather than their magnitude 
that is important. 

The influence of temperature change is manifested on rocks 
in another way. Due to slow conduction the outer surface 
of a rock often maintains a markedly different temperature 



22 



NATURE AND PROPERTIES OF SOILS 



than the inner and more protected portions. This differential 
heating tends to set up lateral stresses which may cause the 
surface layers to peel away from the parent mass. This phe- 
nomena is spoken of as exfoliation. The differential expansion 



S^Vrn DAKOTA . M^^^^SOTA 



NEBRASK# \ i^"^ 




Fig. 4. — Approximate distribution of loess in central United States. 



of the rock minerals of course plays a part in this disintegra- 
tion, although exfoliation readily occurs in rocks which are 
more or less homogeneous. While this form of weathering 
may go on alone, it is much accelerated by chemical action 
and the prying of freezing water. 



SOIL-FORMING PROCESSES 23 

One peculiarity of pure water is that its maximum density 
occurs at 39.2 deg. F. From this point the volume increases 
as the temperature is lowered. Ice, which forms at 32 deg. F., 
thus occupies a greater space than the water from which it 
was derived. The force developed by freezing is equivalent 
to about 150 tons to the square foot or a pressure of 141 
atmospheres. The cracks and crevices of surface rocks in 
humid regions are from time to time filled with moisture. 
Rocks below the surface contain water continuously. The 
change of this water from a liquid to a solid always produces 
marked disintegi'ation. Mountain-top rubble, talus slopes, 
alluvial fans, and similar formations are evidences of such 
action. The load of sediment carried by streams is often due 
to the prying action of temperature change, especially where 
crevice water is present. 

This action of temperature is by no means ended when a 
soil is produced. Freezing and thawing is of tremendous im- 
portance in bettering the physical condition, especially of 
heavy soils. It is to such forces that the farmer owes the 
good tilth of his land. In addition it must be noted that the 
rapidity of chemical change is largely a function of temper- 
ature. The concentration of the soil solution and the avail- 
ability of the nutrient elements thus come under the influence 
of this apparently simple force. 

15. Plants and animals. — While plants and animals unite 
their activities with the processes already mentioned, their 
influence is conflned largely to the soil and the soil material. 
Simple plants such as mosses and lichens grow upon exposed 
rock, there to catch dust and dirt until a thin film of highly 
organic material accumulates. Higher plants sometimes exert 
a prying effect on rock, which results in some distintegration. 
Such influences, however, are of but little import in soil for- 
mation compared to the drastic activities of water, wind, ice 
and temperature change. 

In the soil, roots by their ramifications promote aeration 



24 NATURE AND PROPERTIES OF SOILS 

and drainage, as well as an accumulation and distribution of 
organic materials. Lichens, mosses, and algge play their parts 
in a similar manner. It must be noted, however, that while 
plants tend to preserve and improve the soil tilth, their action 
in this respect is not wholly physical. Decay due largely to 
bacterial action is necessary before the accumulated organic 
matter can improve to any marked degree the physical con- 
dition of the soil. This is only one of the many examples 
illustrating the cooperation of physical and chemical changes 
incident to soil formation. 

Animals influence the soil physically by their burrowing 
propensities. Gophers, squirrels, ants, and the like mix and 
open up the soil, thus providing for the circulation both of 
air and water. Other soil forces, both physical and chemical, 
are markedly encouraged thereby. Earth worms produce 
similar effects. They not only pass great quantities of soil 
through their bodies, but they carry much to the surface. 
This has been estimated as amounting to one or two surface 
inches in a decade. Man also is producing important physical 
changes on the soil and soil material. The plowing under of 
green-manures, crop residues and farm manure, the addition 
of lime and fertilizers and the tillage incident to cropping 
have much to do with the physical changes, which are con- 
tinually occurring in the soil. 

16. Oxidation and deoxidation. — Scarcely has the disin- 
tegration of rock begun than its decomposition is also appar- 
ent. This is especially noticeable in humid regions where the 
chemical and physical processes of soil formation are par- 
ticularly active and markedly accelerate each other. Of the 
chemical forces, oxidation is usually, especially near the sur- 
face, the first to be noticed. It is particularly manifest in 
rocks carrying iron in the sulfide, carbonate or silicate forms. 
The sulfide, although widespread, is less important in pro- 
moting rock decay than the other combinations. The oxida- 
tion of iron in any form is indicated by a discoloration of the 



SOIL-FORMING PROCESSES 25 

affected roek, which from the first is streaked with iron oxide. 
The mica, amphibole, pyroxene and garnet groups are par- 
ticularly affected, until, as the process continues, these min- 
erals waste away into unrecognizable forms so weakening the 
rock as to cause it to crumble easily. The way is now open 
for vigorous chemical and physical changes of all kinds. Oxi- 
dation may be illustrated chemically, using olivine as the 
mineral decomposed. It is to be noted that the first step is 
the assumption of water and the production of serpentine and 
ferrous oxide. The latter quickly changes to the susquioxide. 

3MgFeSi04+2H20=H,Mg3Si209-fSi02+3FeO 
Olivine Water Serpentine Silica Ferrous 

Oxide 
4FeO + Oo = 2Fe203 (red) 
Ferrous Oxygen Ferric Oxide 
Oxide 

Deoxidation is the reverse of oxidation, being a reduction 
of the amount of oxygen present in the compound. With 
hematite it might occur as follows : 

2Fe203 — O2 = 4FeO 
Ferric Oxide Oxygen Ferrous Oxide 

In a similar way, other oxides and salts may be reduced by 
the withdrawal of oxygen. This action occurs in poorly 
drained soils or in soil very rich in organic matter. It is 
generally apparent in forest soils just below the organic sur- 
face layer. Here the leaching downward of small quantities 
of organic acids has been sufficient to develop a definite grey- 
ish zone, varying both in color and depth. The bleaching of 
sands, shales, sandstones, and clays may often be due to 
deoxidation rather than the actual removal of ferric iron. 
No great importance need be attached to deoxidation either 
in soil formation or in the chemical processes which continue 
to affect the soil after it is definitely developed. 



26 NATURE AND PROPERTIES OF SOILS 

17. Carbonation. — The process of oxidation is almost al- 
ways accompanied by the action of carbon dioxide. This gas 
is a constituent of the air and is a product of the organic 
decay which vigorously progresses in most soils. It occurs 
in large amounts in rain water, especially in warm climates. 
It increases the solvent action of water by actively engaging 
in chemical reactions, producing carbonates and bicarbonates 
with the various rock and soil bases. The decomposition of 
orthoclase and muscovite mica into kaolinite and carbonates 
is as follows: 

2KAlSi,0s + 2HoO + CO, = H^AUSi^Og + K0CO3 + 4Si02 
Orthoclase Water Carbon Kaolinite Potassium Silica 
Dioxide Carbonate 

2H2KAl3Si30i. + CO, + 4H2O = SH.Al^SiaOg + K2CO3 

Muscovite Carbon Water Kaolinite Potassium 

Dioxide Carbonate 

Under certain conditions decarbonation may occur. When- 
ever the processes of weathering produce either mineral or 
organic acids carbonates are rapidly decomposed. The 
presence of unsaturated aluminum silicates may also rapidly 
promote decarbonation by absorbing the base and liberating 
the acid radical. This latter reaction is of especial importance 
in soil. 

18. Hydration. — All the chemical transformations above 
discussed depend on the presence of a certain amount of 
water, especially if rapid changes are to occur. The illus- 
trative reactions already cited indicate this. Oxidation pro- 
ceeds but slowly in a dry atmosphere, water being necessary 
as a catalytic agent. In the carbonation of the potash of 
orthoclase and mica, water enters into the reactions, produc- 
ing not only kaolinite but also potassium hydroxide, which is 
later changed to the carbonate. 

Water functions in the chemical changes of rock and soil 



SOIL-FORMING PROCESSES 27 

ill another way — as water of combination.^ The process is 
called hydration. While hydration usually proceeds or ac- 
companies oxidation and carboiiation, thus making them pos- 
sible, it often, unlike these transformations, occurs at great 
depths and may be practically the only change that the rock 
minerals have undergone. Many minerals, especially the oliv- 
ine, feldspar and mica groups, are so affected. They become 
soft and lose their luster and elasticity on the assumption of 
this chemically combined water. Considerable increase of 
bulk occurs during the transition of the rock to soil. The 
latter change has no small physical significance. This hydra- 
tion is particularly effective in encouraging other kinds of 
chemical decay. In addition to the examples already cited, 
the change of hematite to limonite, which occurs to a greater 
or less degree in every soil wliere the sesquioxide is present, 
is worthy of note : 

2Fe203 -f- 311,0 = 2Feo03 . 3H,0 
Hematite Water Limonite (yellow) 

When the products of weathering dry out due to varying 
weather conditions, dehydration may occur. Thus limonite 
may readily reduce to a lower hydrate or to hematite. 

19. Solution. — It is quite evident that while weathering 
and erosion produce many compounds of a very complex char- 
acter, there is a tendency toward simplification and, as water 
is universally present, some solution occurs. Such bases as 
calcium, magnesium, sodium and potassium are found in the 
water that circulates in rocks, soil materials and soils. These 
bases, when in solution, are generally combined as chlorides, 
phosphates, nitrates, carbonates, and the like. Carbon dioxide 
intensifies to a marked degree the solvent action of water and 
consequently increases its power as a weathering agent. The 

* Note carefully the difference between hydration and the production 
of an hydroxide. The former is the more important as a soil phenome- 
non. 



28 NATURE AND PROPERTIES OF SOILS 

atmosphere carries about .03 per cent, of carbon dioxide by 
volume, while considerable amounts are brought down on 
rocks and soil by rain and snow. Traces of nitric and sul- 
furic acid are also found in rain water. The carbon dioxide 
produced within the soil by decaying organic matter keeps 
the concentration of this gas high at points where it can act 
most effectively. 

Solution/ accelerated both by mechanical and chemical 
means, is of particular importance in two directions. In the 
first place, it allows a continual loss of plant nutrients not 
only as the soil is being formed but after it becomes a proper 
medium for plants. This constant drain accounts for the 
deficiency of certain elements in the soil and the need in cer- 
tain eases of such additions as lime and fertilizers. On the 
other hand, this solution, however wasteful, is necessary since 
plants absorb nutrients from the soil only in soluble form. 
The concentration and composition of the materials in the 
soil water is thus a function of solution, which is a culmina- 
tion of the activities of the soil processes already discussed. 

20. General statement of soil formation. — By a very 
complicated coordination the mechanical and chemical forces 
of weathering reduce the solid rock to small fragments and 
mix therein the necessary organic matter. The process slowly 
proceeds until a suitable medium for the growth of higher 
plants is produced. As a rule, the chemical processes are in- 
complete and all stages of decay are exhibited. This is for- 
tunate, as solution may thereby continue to renew the nutrients 
in the soil-water for a long period and thus maintain the 
continuous productivity of the soil. 

The products of disintegration and decomposition are com- 
monly classified into two general groups, sedentary and trans- 

* While the formula for water is generally given as H^O the molecule 
is not as simple as this, being at low temperature as high as (HjO)!, 
The remarkable power of water as a solvent may be due to extra oxygen 
valences as well as to the high dielectric constant which favors ioniza- 
tion, thus hastening chemical reaction. 



SOIL-FORMING PROCESSES 



29 



ported. The former remains in place, being the rock residuum 
in which organic matter accumulates. Residual clay is an 
example. The second group, on the other hand, in addition 
suffers transportation and is represented by the soils arising 
from glacial drift, alluvial accumulations, aeolian deposits, 
and the like. In the first case, the soil is derived from a single 
lithologic unit ; in the second place, the assorted and blended 
materials are from many sources. A general statement of 
the formation of a residual soil ^ is obviously the easier to 




Fig. 5. — The gradual transition of country rock into residual soil by 
weathering in. situ. 

make. Such a statement adequately covers every process in 
the production of a transported soil except the disintegra- 
tion, assortment, and solution due to translocation, (See 
Fig. 5.) 

"The changes that a rock undergoes in forming a residual 
soil are first a physical breaking down, accompanied by certain 
chemical transformations, which consist in the hydration of 
a portion of the feldspars, micas and similar minerals; the 

^ Buekman, H. O., The Formation of Residual Clay; Trans. Amer. 
Cer. Soc, Vol. XIII, p. 362. Feb., 1911. 



30 NATURE AND PROPERTIES OF SOILS 

oxidation and hydration of a part of the combined iron ; and 
a carbonation and solution of a large proportion of the soluble 
bases. These processes are hastened and the whole mass 
evolved into a soil by the admixture and decay of certain 
amounts of organic matter. ' ' ^ 

21. Variation of soil formation with climate. — It may 
be seen readily that the activity of the various soil-forming 
agencies will fluctuate with climate. A comparison of weath- 
ering and erosion in an arid and a humid region will illustrate 
the point at issue. Under arid conditions, the physical forces 
will dominate and the resultant soil will be coarse. Tempera- 
ture changes, wind action and the influence of animals will 
be almost the sole agents. In a humid region, however, the 
forces are more varied and practically the full quota will be 
at work. Chemical decay will accompany disintegration and 
the result will be shown in the greater fineness of the product. 
The separate minerals will also show the change of color and 
loss of luster so characteristic of chemical action. A granite, 
for example, is a very insoluble rock, compared with a lime- 
stone, and in a humid region, where chemical agencies are 
dominant, it will be markedly more resistant. If, however, 
these rocks are exposed in an arid region, where physical 
weathering is potent, the results will be entirely different. 
The limestone, being homogeneous, will not be affected mark- 
edly by temperature changes, but the stresses set up in granite 
must ultimately reduce it to fragments. 

Arid soils, besides being rather coarse, are generally rather 
uniform, there being little difference between soil and subsoil. 
The soils of humid regions are usually of fine texture, par- 
ticularly in residual sections, since the chemical agencies have 

^ It is well to remember that synthetic processes as well as forces of 
simplification and dissolution are active in soil formation. The soil 
features that result are of two kinds, hereditary and acquired. The 
former develop through geological forces, the latter through the activity 
of true soil processes. 



SOIL-FORMING PROCESSES 



31 



been so active. Various colors may develop because of oxida- 
tion, hydration, and the presence of organic matter. Such 
soils usually are not excessively deep, and are likely to be 
underlaid by subsoils heavier than the surface. The general 
physical condition and tilth of arid soil is uniformly better 
than that of regions of plentiful rainfall. 

Chemically, because of less leaching, the arid soils contain 
more of the important mineral elements. The following 
analyses bring out the differences in a striking manner : 



Table II 

COMPARATWE ANALYSES OF ARID AND ' HUMID SOILS^ 





Arid Soils 


Humid Soils 


CONSTITUENTS 


AVKRAGE OF 


Average of 




313 Samples 


466 Samples 


Insoluble 


77.82 


88.24 


AI2O3 


7.89 


4.30 


Fe,03 


5.75 


3.13 


CaO 


1.36 


.11 


K2O 


.73 


.22 


P3O. 


.12 


.11 


MgO 


1.41 


.23 


Volatile 


4.94 


3.64 



It is immediately apparent that the arid soil is poorer in 
silica than the humid soil, but richer in iron and alumina, in- 
dicating a less vt^eathered condition of the feldspars. Due to 
a greater amount of leaching, the humid soil is much lovt^er 
in phosphoric acid, lime, magnesia, and potash. The humus 
in arid soils is somewhat lower than in the soils under better 



^Hilgard, E. W., Die Boden arider und humider Lander; Internat. 
Mitt. Bodenkunde, Bd. I, pp. 415-529. 1912. 



32 NATURE AND PROPERTIES OF SOILS 

conditions of rainfall, as one would naturally expect. The 
amount of easily soluble material is higher in arid regions, 
due to the lack of rain and the tendency for soluble salts to 
accumulate. Biologically, organisms are active at greater 
depths^ in arid than in humid regions, because of the loose 
structure of arid soils and because of their good aeration. 
Such soils are seldom water-logged except from improper ir- 
rigation. In humid regions bacterial action is limited very 
largely to the surface foot of soil, since only there are the 
aeration and the food conditions adequate. The intensity of 
biological activity in arid soils is very largely governed by 
moisture, and when moisture conditions are satisfied, bacterial 
changes may be expected to take place rapidly. 

22. Special cases of soil formation. — Having compared 
the weathering of granite and limestone under different cli- 
matic conditions, it is interesting to note the quantitative chem- 
ical changes of these rocks as they are reduced residually to 
soil under humid conditions. The following analyses- indicate 
the elements that are likely to be lost to the greatest extent 
during the process. (See Tables III and IV, page 33.) 

The soil resulting from the decay of the granite was a deep 
red clay, with numerous quartz grains present. The soil 
from the limestone was very plastic and high in silicate silica. 
Leaching has probably gone on to a very great extent in both 
soils. It is noticeable in both cases that the bases, such as 
calcium, magnesium, sodium, and potassium, have suffered 
severe losses. The carbonate has almost wholly disappeared 
from the limestone clay, indicating that a residual soil from 
such a rock will probably need an application of lime. (See 
Figs 6 and 7, pages 34 and 35.) 

^Lipman, C. B., The Distribution and Activities of Bacteria in Soils 
of the Arid Region; Univ. Calif., Pub. in Agr. Sci., Vol. I, No. 1, pp. 
1-20. 1912. 

' Merrill, G. P., Weathering of Micaceous Gneiss; Bui. Geol. Soe. 
Amer., Vol. 8, p. 160. 1879. 



SOIL-FORMING PROCESSES 
Table III 

FRESH GRANITE AND ITS RESIDUAL CLAY 



33 



Constituents 


EOCK 


Soil 


Percentage 

LOST^ 


SiOa 


60.69 


45.31 


52.45 


A1303 


16.89 


26.55 


.00 


Fe303 


9.06 


12.18 


14.35 


CaO 


4.44 


.00 


100.00 


MgO 


1.06 


.40 


74.70 


K,0 


4.25 


1.10 


83.52 


Na^O 


2.82 


.22 


95.03 


P2O3 


.25 


.47 


.00 


Ignition 


.62 


13.75 


gain 



Table IV 

VIRGINIA LIMESTONE AND ITS RESIDUAL CLAY ^ 



Constituents 


Rock 


Soil 


Percentage * 
Lost 


SiOg 


7.41 


57.57 


27.30 


Al,03 


1.91 


20.44 


.00 


Fe^Og 


.98 


7.93 


24.89 


CaO 


28.29 


.51 


99.83 


MgO 


18.17 


1.21 


99.38 


K,0 


1.08 


4.91 


57.49 


NaaO 


.09 


.23 


76.04 


P2O5 


.03 


.10 


68.78 


CO2 


41.57 


.38 


99.15 


H2O 


.57 


6.69 


gain 



*The percentage loss of any constituent is calculated as follows: 
A X 100 

= X 100 — X = % Lost. 



BX 



'Diller, J. 



A = % any constituent in residual material. 
B = % same constituent in fresh rock. 
C = % of the constant constituent in residual soil. 
D = % of the constant constituent in fresh rock. 
S.. Educational Series of Bock Specimens; U. S. Geol. 



Survey, Bui. 150, p. 385. 1898. 



34 NATURE AND PROPERTIES OF SOILS 

The analyses indicate that the soil from the granite does 
not differ greatly from the original rock, except in the loss of 
bases, assumption of water, and increase of organic matter. 
The soil from the limestone presents greater differences, due 



'60.6ci=z==^z2i::::"_v_".:::::"^ 






,38.71 



AlgO'; 



CaO + l ^'^ 
MtjO 



KgO 



.4 1 
( 4.Z 

l.l 



(2.8C 
1.2. 



NazO 

60 



CZ3 ' ' GRANITE 

■{^RESIDUAL SOIL 



1^.7 



Fig. 6. — Diagram showing the composition of fresh granite and its 
residual soil. Note the marked hydration of the soil. 



to the disappearance of the calcium carbonate. The analyses 
of the two soils resemble each other rather closely in spite of 
their widely different sources. Since weathering, especially 
residual weathering, causes a loss of basic materials and 



SOIL-P^ORMING PROCESSES 35 

thereby favors the accumulation of silica, alumina and iroii, 
all soils as they age tend to approach each other in chemical 
composition. Yet, owing to a differe^ice in the adjustment 
of the forces at work and to the time element, no two soils 



% 



S'°2 {5X6 



F«2 05+12.90=] 



Ca0+r46.0l 
MgO 1 1.71 



coe 1^'; 



4t.6C 
41 



LIMESTONE 
RESIDUAL S<iIL 



Fig. 7, — Diagram showing the composition of limestone anrl its residual 
soil. Note the excessive loss of lime and carbon dioxide in soil 
formation. 



will ever be exactly alike. Soils will differ from the original 
rock and from one another according to the intensity and 
character of the weathering and erosive forces and to the 
constitution of the parent minerals. 



36 NATURE AND PROPERTIES OF SOILS 

23. Red and yellow colors of soil.^ — The presence of 
iron, as already noted, is a very important factor in rock 
weathering, and the discoloration due to its presence is an 
unfailing indication of chemical decay. The iron in minerals 
occurs usually as ferrous oxide, which is soluble, especially 
if the water circulating among the rock fragments carries 
carbon dioxide. When this water comes in contact with the 
air its excess of carbon dioxide is discharged and the oxides 
and carbonates of iron are deposited. Under this condition 
oxidation goes on rapidly, and the iron passes to the ferric 
state and becomes insoluble. Thus it may be seen that iron 
imparts a fatal weakness to rocks and minerals in which it 
exists, due to its solubility; yet from the oxidation that it 
undergoes it tends to persist and accumulate in soils. The 
more iron a mineral or rock contains the more susceptible it 
is to weathering. 

The red and yellow soils of the southern states frequently 
excite comment, especially as a difference in fertility is popu- 
larly recognized, the red surface soil with a red subsoil being 
considered more fertile than a similar soil with a yellow sub- 
soil. This is probably due to differences in hydration of 
the iron oxides.' 

The soil temperatures, particularly in tropical and sub- 
tropical regions, have first tended fully to oxidize and hydrate 
the iron, and then to dehydrate the soil at the surface into 
the deep red color, leaving the subsoil yellow and causing 
the contrasts so markedly evident. Soils having a yellow 
surface soil are generally considered to be older and more 
weathered than those where the red is well developed. When 

^Eobinson, W. O., and McCaughey, W. J., The Color of Soils; U. S. 
Dept. Agr., Bur. Soils, Bui. 79, p. 21. 1911. 

=■ Crosby, W. O., Colors of Soils; Proc. Boston Soc. Nat. Hist., Vol. 23, 
pp. 219-222. 1875. Merrill, G. P., Bocks, Bock Weathering and Soils; 
p. 375. New York, 1906. Van Bemmelen, J. M., Beitrage zur Eenntnis 
der Verioitterungsprodukte der Silicate in Ton-, Vulkanischen-, und 
Laterite-Boden; Zeit. Anorg. Chem., Bd. 42, Steite 290-298. 1904. 



SOIL-FORMING PROCESSES 



37 



these old residual soils are poorly drained a well defined 
mottling develops, especially in the subsoil, due to the ir- 
regularities of aeration. 

The compositions of hematite and of the limonite group 
indicate the possibility of a progressive change from red to 
yellow by hydration : 



Hematite FegOg 



Limonite 
Group. . 



fTurgite 2Fe203. H^O 

Goethite Fe^Og. H^O 

Limonite 2Fe203 . Sll^O 

Xanthosiderite' . Fe203.2H20 
Limnite Fe.,0,.3H20 



Red 



Yellow 



24. Practical relationships of weathering. — Soil-form- 
ing processes fortunately remain intensely active after the 
soil has been produced. The physical agencies especially 
tend to loosen and fine the soil, contributing largely to its 
tilth. The farmer encourages such influences by plowing his 
land and by other tillage operations. The addition of organic 
matter is another means whereby these physical changes may 
be influenced. Granulation in a clay soil is due almost en- 
tirely to natural agencies. AVere it not for such activities 
the soil would soon become physically unfit as a foothold for 
plants. The continual chemical changes, culminating in solu- 
tion, provide the soil-water with plant nutrients not only 
in suitable concentration but in correct proportion. By 
slow processes, over geologic periods. Nature has provided 
us with soil and by the same slow processes Nature is at- 
tempting to maintain the fertility of her creation. The en- 
couragement and control of such agencies is of no small 
moment in practical soil management. 



CHAPTER III 

THE GEOLOGICAL CLASSIFICATION OF SOILS 

Weathering must be considered as affecting soils, whether 
they are in motion or at rest. This gives rise to two general 
classes of soil materials — those that have not been shifted 
far from their original situation and those that have suffered 
considerable translocation. These two general groups, desig- 
nated as sedentary and transported, are subject to subdivision 
as follows : ^ 

o 1 . /Residual 
Sedentary i ^ , 

"^ ICumulose 



Transported 



Gravity Colluvial 

r Alluvial 

Water . . . . i Marine 

[ Lacustrine 

Ice Glacial 

Wind ^olian 



25. Residual soils. ^ — This group of soils covers wide 
areas of arable regions, especially in the tropics and sub- 
tropics, and comes from many kinds of rock. Residual soils 
are, in the main, old soils, usually the oldest with which we 
deal in agricultural operations, although some residual soils 
are comparatively young. Since they are formed in situ, 

^Merrill, G. P., EocTcs, BocJc Weathering and Soils, p. 288; New York, 
1906. 

^ For a full discussion of the origin and characteristics of the soils 
of the United States see Marbut, C. F. et al., Soils of the United States; 
U. S. Dept. Agr., Bui. 96. 1913. For the soils of the Southern States, 
consult Bennett, H. H., The Soils and Agriculture of the Southern 
States; New York, 1921. 

38 



GEOLOGICAL CLASSIFICATION OF SOILS 39 

the rocks that underlie them, if sound, often given some clue 
to the character and composition of the parent material.^ 
Under such conditions the changes that a rock undergoes in 
forming a soil may be studied to the best advantage. 

Residual soils are usually non-stratified and present a 
heterogeneous mass of material, grading from a true soil, 
with its normal content of organic matter, downward through 
the typical soil material to the unweathered country rock 
below. Since such soil has been subject to leaching for long 
periods, a very large amount of its soluble materials have 
been washed out, tending to leave high percentages of the 
persistent elements, such as silica, iron and aluminum. The 
preceding discussion of soil formation has already emphasized 
this phase sufficiently. 

The great age of residual soils has given opportunity for 
very thorough oxidation, so that much of the iron has changed 
to hematite or to the hydrated limonite group. The yellow 
color of the latter group is indicative of greater age than the 
former. Since almost all soil material contains considerable 
iron the prevailing colors of residual soils are reds and yel- 
lows, depending on the degi'ee of oxidation and hydration. 
Grays, browns, and blacks often occur, however, where oxida- 
tion has not progressed or where organic matter is present in 
amounts sufficient to mask the iron coloration. 

As residual soils have been subjected to intense physical 
and chemical weathering, the particles have been reduced 
to a very fine state of division. Over residual areas the 
heavier types, such as silt loams, clay loams and clays pre- 
dominate. Sands and sandy loams may occur, however, 
when the parent rock carried considerable quartz and a low 
percentage of clay-producing minerals, such as feldspar, horn- 
blende and augite. Soils from limestones, granites, and 

^Eesidual soils are not always derived from rock similar to that 
directly underlying the soil as is often assumed. When the present 
bed rock is much different from the stratum which gave rise to the 
soil, the soil is said to be " inherited. ' ' 



40 NATURE AND PROPERTIES OF SOILS 

gneiss ^ are generally clayey in nature, although loams and 
even stony loams may occur if the limestone was sandy or 
cherty and if the igneous rocks carried much quartz. Dolo- 
mites weather more slowly than limestone and often give 
rise to gravelly and stony types. Sandstone of course pro- 
duces sandy soils, although a soil from an argillaceous sand- 




FiG. 8. — Diagram showing the relationship between the underlying rocks 
and the overlying residual soils. Gettysburg, Pa. (After Emerson.) 



stone may be rather heavy. Quartzite and slaty soils are 
generally shallow, and unfavorable, both in texture and fer- 
tility, for crop growth. Soils from basic igneous rocks, such 
as diorite and basalt, generally produce sticky reddish or yel- 
lowish clays containing little quartz. Rocks that carry con- 
siderable mica, such as schists, give rise to highly micaceous 
soils. 

^ For a complete discussion of the influence of various parent rocks on 
the resultant residual soil see Emerson, H. L., Agricultural Geology, 
Chap. IV; New York, 1920. 



GEOLOGICAL CLASSIFICATION OP SOILS 41 

The following analyses ^ show the general chemical char- 
acter of surface residual soils and the variations that may 
be expected: 

Table V 



Constituents 


1 


2 


3 


4 


SiO^ 


66.49 


76.71 


74.33 


70.99 


Al,03 


17.11 


12.85 


11.00 


11.39 


Fe,03 


7.43 


2.81 


4.64 


4.23 


TiO, 


1.02 


.41 


1.04 


1.28 


CaO 


.36 


.08 


1.13 


.93 


MgO 


.31 


.29 


.69 


1.08 


K^O 


.62 


3.26 


1.57 


2.71 


Na^O 


.16 


.39 


1.53 


.82 


P20„ 


.17 


.05 


.16 


.19 


SO3 


.07 


.12 


.15 


.34 


Organic matter 


1.26 


1.78 


1.99 


.93 



The organic matter of residual soils largely depends, in 
amount and condition, on climatic factors. If rainfall and 
temperature, for example, are favorable for the rapid and 
continued development of a natural vegetation the soil will 
be rich in humus, so rich at times as to mask to a certain 
extent the red color so characteristic of such soils. If plants 
do not grow well on this soil, however, it will be low in organic 
matter and probably in poor physical condition. Residual 
soils vary greatly in their general characteristics, especially as 
to crop productivity. 

Residual soils are of wide distribution in the United States, 
particularly in the eastern and central parts, although great 

^ Robinson, W. O., The Inorganic Composition, of Some Important 
American Soils; U. S. Dept. Agr., Bui. 122, Aug. 1914. 

1. Cecil clay, from granite and gneiss. Charlotte, N. C. 

2. York silt loam, from schists. Bethany, S. C. 

3. Penn silt loam, from sandstone. Morristown, Pa. 

4. Hagerstown loam, from limestone. Conshohocken, Pa. 



42 NATURE AND PROPERTIES OE SOILS 

areas are found in the West as well. A glance at the soil 
map of this country shows four great eastern and central 
provinces — the Piedmont Plateau, the Appalachian Moun- 
tains and Plateaus, the Limestone Valleys and Uplands, and 
the Great Plains Region. The first three groups alone oc- 
cupy 10 per cent, of the area of the United States. The age 
of these soils varies in the order named, showing that, while 
they are very old as compared with other soils yet to be dis- 
cussed, there may be vast periods of geologic time between 
their beginnings. As a matter of fact, there is probably a 
greater difference in age between the soils of the Piedmont 
Plateau and those of the Great Plains Region than has elapsed 
since the latter were formed. (See Fig. 9.) 

26. Cumulose soils. — At relatively recent periods shal- 
low lakes, ponds, and basins have been formed, partly by 
stream action, partly by marsh conditions along sea or lake 
coasts, or by glaciation, a common origin in northern United 
States and Canada. The highly favorable moisture rela- 
tions along the banks of such standing water has encouraged 
the growth of many plants, such as algOB, mosses, reeds, flags, 
grass, and even larger types of vegetation. These plants 
thrive, die and fall down to be covered by the water in which 
they grew. The water shuts out the air, prohibits rapid 
oxidation, and thus acts as a partial preservative. The decay 
that does go on is largely through the agency of fungi and 
anaerobic bacteria, that break down the tissue, and liberate 
certain gaseous constituents. As the process continues the 
organic mass becomes dark or even black in color. 

Accumulations of this nature are dotted over the entire 
country. Their size may vary from a few acres to several 
thousand. Along streams the old abandoned beds offer ready 
opportunity for the beginning of such accumulations. 
Marshes either salt or fresh often contain such deposits. 
Shallow basins produced by the scraping or damming action 
of glaciers are frequently occupied by such material. In the 




]?JG_ 9, — Map showing the soil provinces and soil regions of the United States. Th 
Valleys and Uplands are residual. The soil regions of western Uni 




ils of the Piedmont Plateau, Appalachian Mountains and Plateaus and the Limestone 
States contain soils of many different origins. (Bui. 96, Bur. Soils.) 



GEOLOGICAL CLASSIFICATION OF SOILS 43 

last named ease the beds are more or less independent of 
topography, and may be found on hillsides as well as in lower 
lands. 

Cumulose materials may be grouped under two heads, peat 
and muck. The only difference is in their state of decay. 
In peat the stem and leaf structure of the original plants 
can still be detected, and identification is quite possible. In 
muck, however, the plant tissue has lost its identity as such 
and is merged into a complicated and indefinite mass of 
organic material.^ 

The composition of peat and muck may be much altered 
by the washing-in of mineral matter. In some cases the beds 
may be from 90 to 95 per cent organic, while in other cases, 
due to this foreign material, the percentage may drop as low 
as 20 per cent giving a black or swamp marsh mud. 

The analyses given illustrate the composition of some rep- 
resentative cumulose soils. (See table VI, page 44.) 

Peat and muck are often of large extent - and become of 
extreme value when drained, especially if they are near a 
good market. They are of peculiar value in trucking oper- 
ations, being adapted to such crops as onions, celery, lettuce, 
and the like. Usually they must not only be provided with 
drainage, but must also be treated with fertilizers carrying 

^ The term ' ' muck ' ' is often used interchangeably with peat. Tech- 
nically it is best to limit the former term to those peats which are very 
thoroughly decomposed or contain a high proportion of mineral matter. 
Chemically muck is often used in reference to soils containing from 20 
to 50 per cent, of organic matter, while peat is confined to soils in which 
the amount of organic constituents is above 50 per cent. According to 
such a definition most cumulose soils are peats instead of muck. The 
term "muck" is so popular, however, that in the United States its use 
will continue in spite of the technical distinctions that have been, 
established. 

' Alway reports the following figures : 

Germany .... 5,000,000 acres Wisconsin . . . 3,000,000 acres 

Sweden 12,000,000 " Ohio 175,000 " 

Minnesota ... 7,000,000 " Canada 22,000,000 " 

Alway, F. J., Agricultural Value and Beclamation of Minnesota Peat 
Soils; Minn. Agr. Exp. Sta., Bui. 188, 1920. 



44 NATURE AND PROPERTIES OF SOILS 

Table VI 

COMPARATIVE CHEMICAL COMPOSITION OF A PRODUCTIVE MIN- 
ERAL SOIL AND CERTAIN REPRESENTATIVE PEAT 
AND MUCK SOILS. 



Soils 


Organic 
Matter 


Mineral 
Matter 


N 


P2O, 


K,0 


CaO 


Representative 














mineral soil 


5.00 


95.0 


.25 


.15 


1.80 


.70 


Minnesota peat ^ 


94.00 


6.0 


1.70 


.16 


.04 


.31 


Minnesota peat ^ 


59.00 


40.3 


2.35 


.36 


.17 


2.52 


Minnesota Muck ^ 


50.6 


49.4 


1.92 


.40 


— 


— 


Minnesota Muck ^ 


41.4 


58.6 


1.78 


.21 


— 


— 


Florida peat ^ 


68.4 


31.6 


2.63 


.20 


.17 


— 


Canadian peat ^ 


74.3 


25.7 


2.19 


.20 


.16 


— 


German peat * 














(Low lime) 


97.0 


3.0 


1.20 


.10 


.05 


.35 


German peat * 














(High lime) 


90.0 


10.0 


2.50 


.25 


.10 


4.00 



phosphorous and, especially, potash. It is also a good prac- 
tice to start vigorous decay by the applicaton of barnyard 
manure, as the nitrogen carried by muck soils is usually not 
very readily available to plants.^ 

^ Alway, F. J., Agricultural Value and Reclamation of Minnesota Peat 
Soils; Minn. Agr. Exp. Sta., Bui. 188, Mar., 1920. 

'Pickel, G. M., Muck: Composition and Utilisation; Fla. Agr. Exp. 
Sta., Bui. 13, 1891. 

^ Kept. Can. Exp, Farms, 1910. Rept. of chemist, p. 160. 

* Fleischer, M., Die Anlage und die Bewirtscliaftung von Moorwiesen 
und Moorweiden; Berlin, 1913. 

"Publications regarding the practical utilization of peat and muck 
lands: Robinson, C. S., Utilization of Much Lands; Mich. Agr. Exp. 
Sta., Bui. 273. 1914. "Whitson, A. R., et al., The Improvement of Marsh 
Soils; Wis. Agr. Exp. Sta., Bui. 205. 1914. Stevenson, W. H., and 
Brown, P. E., Improving Iowa's Peat and Alkali Soils; la. Agr. Exp. 
Sta., Bui. 157. 1915. Smalley, H. R., Management of Much Land 
Farms in Northern Indiana and Southern Michigan; U. S. Dept. Agr., 
Farmers' Bui. 761. 1916. Thompson, H. C, Truck Growing on Peat 
Soils; Jour. Amer. Peat Soc, Vol. II, No. 3, pp. 113-125. 1918. 
Alway, F. J., Agricultural Value and Beclamation of Minnesota Peat 
Soils; Minn. Agr. Exp, Sta,, Bui. 188. Mar., 1920. 



GEOLOGICAL CLASSIFICATION OF SOILS 45 

In many cases muck and peat are underlaid at varying 
depths by a soft impure calcium carbonate, called bog-lime/ 
Such a deposit may come from the shells of certain of the 
Mollusca, which have inhabited the basin, or from aquatic 
plants, such as mosses, algJE and species of Chara. In car- 
bonated water these plants become incrusted with calcium 
carbonate, possibly because of their ability to absorb carbon 
dioxide," thus precipitating the carbonate. In most cases 
this carbonate accumulation is due to a combination of the 
two agencies. Such material, because of its richness in cal- 
cium, is valuable as a soil amendment, and often, where it is 
found pure enough in quality and in sufficiently large quan- 
tities, it is handled commercially. 

27. CoUuvial soils. — This soil is formed in regions of 
precipitous topography, and is made up of fragments of rocks 
detached from the heights above and carried down the slopes 
by gravity. Talus slopes, cliff debris, and other heterogeneous 
rock detritus are examples of colluvial soil. Avalanches are 
made up largely of such material. 

As the physical forces of weathering are most active in the 
formation of these soils the amount of solution and oxidation 
is usually small. The upper part of the accumulation ex- 
hibits physical action to the greatest extent, the particles being 
angular, coarse, and comparatively fresh; farther down the 
slope the material may merge by degrees into ordinary soil.^ 
Such soils are usually shallow and stony, and approach the 
original rock in color unless large amounts of organic matter 
have accumulated. Colluvial soils are not of great importance 

^ Bog-lime is often spoken of as marl. Marl, as used by the geologist, 
refers to a calcareous clay of variable composition. Bog-lime, when it 
contains numerous shells, is often termed shell-marl. See Stewart, C. F., 
The Definition of Marl; Econ. Geol., Vol. 4, No. 5, pp. 485-489, 1909. 

== CaH^C 003)2 ?:± CO2 + H,0 -f CaCOa. 

^ Colluvial soils generally merge so gradually into alluvial fans that 
the line of separation is difficult to establish. When the area of col- 
luvial material is small, as it usually is, it is best included in the fan 
soils. 



46 NATURE AND PROPERTIES OF SOILS 

agriculturally because of their small area, their inaccessibility, 
and their unfavorable physical and chemical characteristics. 

28. Alluvial soils. ^ — In considering- water as a soil-form- 
ing agency, it was found to have both cutting and transporting 
powers. Alluvial soils are the direct result of these activities, 
especially the latter. The carrying power of water varies di- 
rectly as the sixth power of the velocity ; so that doubling the 
velocity increases the transportive ability sixty-four times. 
Obviously any checking of a stream's velocity will force it to 
deposit its load, the larger particles first and the finer as the 
current becomes more sluggish. With changes of velocity dif- 
ferent grades of material are laid down, giving rise to strati- 
fication, one of the important characteristics of an alluvial 
soil. Streams never deposit, either along their course or at 
their delta, all of their sediment. Many tons of material both 
in suspension and in solution are discharged yearly into the 
ocean.^ 

There are three general classes of alluvial soils: (1) flood 
plain deposits, (2) deltas, and (3) alluvial fans. As the 
outlet of a stream is approached, its gradient generally be- 
comes less inclined and its current is slackened. In a large 
stream this often means an aggrading of the channel due to 
the deposited material. A stream on a gently inclined bed 
usually begins to swing from side to side in long, gentle 
curves, depositing alluvial material on the inside of the curves 
and cutting on the opposite banks. This results in oxbows and 

^ If a detailed discussion regarding alluvial, marine, and glacial activi- 
ties is desired, the following books will be helpful: Tarr, E. S., and 
Martin, L. M.^ College PhysiograiJJiy ; New York, 1918. Pirsson, L. V,, 
A Text Boole of Geology, Part I; New York, 1915. Emerson, H. L., 
Agricultural Geology; New York, 1920. The considerations of river 
and stream action by Russell and Davis are classical: Russell, I. C, 
Rivers of North America ; New York, 1898. Davis, W. M., The Rivers 
and Valleys of Pennsylvania ; Geological Essays, Boston, 1909. 

* Streams each year discharge into the ocean, on the average, 100 tons 
of soluble matter for every square mile of drainage area. The Mississippi 
River pours into the Gulf of Mexico each year 406,250,000 tons of sedi- 
ment, not to mention a vast amount of soluble salts. 



GEOLOGICAL CLASSIFICATION OF SOILS 47 

lagoons, -which are ideal not only for the further deposition 
of alluvial matter but also for the formation of cumulose soils. 
This state of meander naturally increases the probability of 
overflow in high water, a time when the stream is carrying 
much suspended matter. This suspended material is deposited 
over the flooded areas; the coarser near the channel, building 
up natural levees; the finer sediment farther away in the 
lagoons and slack water. 

Due to a change in grade, a stream may cut down through 
its already well-formed alluvial deposits, leaving terraces on 
one or both sides. Often two, or even three, terraces may be 
detected along a valley, marking a time when the stream-bed 
was at these elevations. On the lower slopes of hills bordering 
valleys the colluvial deposits may touch or even mingle with 
the alluvial, furnishing the stream with some detritus. Flood 
plain soils are variable in character, ranging from sandy loams 
to heavy clays. 

A great deal of the sediment carried by streams is not de- 
posited in the flood plain but is discharged into the body of 
water to which the stream is tributary. Unless there is suffi- 
cient current and wave action the suspended material ac- 
cumulates, forming a delta. Such deposits are by no means 
universal, being found at the mouths of but a small propor- 
tion of the rivers of the world. A delta is generally a con- 
tinuation of the flood plain and as it is built farther and far- 
ther out the stream is forced to aggrade its bed and both 
flood plain and delta are raised. Near the front of the delta 
the land is swampy ; farther back it is higher and may assume 
considerable agricultural importance. 

Where streams descend from mountains or plateaus, sudden 
changes in gradient often occur as the stream emerges in the 
lower lands. A deposition of sediment is thereby forced, giv- 
ing rise to alluvial fans.^ They differ from deltas in their 

* As already noted, alluvial fans and colluvial material are very closely 
related. Soil survey classifications usually do not recognize the latter 
separation. 



48 



NATURE AND PROPERTIES OF SOILS 



location and in the character of their material. The material 
of the latter is generally sandy, more or less porous and well 
drained. Deltas, on the other hand, are characterized by poor 

drainage and by heavy 
soils, silt loams, clay 
loams and clays predom- 
inating. 

Alluvial soils, espe- 
cially those of flood 
plain origin, are com- 
paratively young. Delta 
and first bottom soils are 
usually in need of drain- 
age. Alluvial fans and 
terrace soils are oiten 
loose and open to the 
point of droughtiness. 
The latter group is usu- 
ally not so well sup- 
plied with organic mat- 
ter as are the delta and 
flood plain soils, which 
exist under conditions 
where organic accumu- 
lation is rapid. All allu- 
vial soils are greatly in- 
fluenced by the source 
of the detritus. For ex- 
ample, a red upland soil 
will give a reddish allu- 
vial, while a soil or rock poor in lime will certainly not be 
parent to one rich in that constituent. Alluvial soils are gen- 
erally richer in the essential constituents than the soils from 
which they are a wash, as is shown by the following data 
from North Carolina. 




Fig. 



10. — The flood-plain and delta of the 
lower Mississippi Eiver. 



GEOLOGICAL CLASSIFICATION OF SOILS 49 
Table VII 

CHEMICAL ANALYSES OF TWO ALLUVIAL SURFACE SOILS AND THE 

RESPECTIVE SURFACE SOILS FROM WHICH 

THEY WERE DERIVED.^ 



Constituents 


1 

Alluvial 


2 
Upland 


3 

Alluvial 


4 
Upland 


N 


.073 

.076 

1.697 

1.103 


.048 

.041 

1.330 

.200 


.173 
.118 
.433 
.417 


.038 


P.,05 

ICO 


.027 

.286 


CaO 


.221 



Delta soils, where they occur in any acreage, are very im- 
portant. The deltas of the Mississippi, Ganges, Po, Tigris, 
and Euphrates rivers are striking examples. Egypt, for 
centuries the granary of Rome, bespeaks the fertility of such 
land. Flood plain soils are found to a certain extent along 
every stream, the greatest development in the United States 
occurring along the Mississippi. This area varies from forty 
to sixty miles in width and has a length from Cairo to the 
Gulf of over 600 miles. Such soils are very rich but, if 
they are first bottoms, they require drainage and protection 
from overflow. Alluvial fan soils are found over wide areas 
in arid and semi-arid regions and when irrigated and prop- 
erly handled have proven very productive. They often occur 
in large enough areas in humid regions to be of considerable 

'Williams, C. B., et al., Eeport on the Piedmont Soils; Bui. N. C. 
Dept. Agr., Vol. 36, No. 2, Feb., 1915. 

1. Average of 8 analyses of Piedmont alluvial soils, Congaree 
series, to a large extent a wash from the Cecil. 

2. Average of 71 analyses of Cecil series soils, the typical upland 
soil of the North Carolina Piedmont. 

Williams, C. B., et al., Eeport on the Coastal Plain Soils; Bui. N. C. 
Dept. Agr., Vol. 39, No. 5, May, 1918. 

3. Average of 8 analyses of coastal plain alluvial soils, Johnston 
and Kalmia series. 

4. Average of 165 analyses of Norfolk series soils, the typical 
upland coastal plain soil of North Carolina. 



50 NATURE AND PROPERTIES OF SOILS 

importance. The type of farming and the crops grown on any 
area of alluvial soil will vary with climate, soil conditions, 
and markets. 

29. Marine soils.^ — A great deal of the sediment carried 
away by stream action is eventually deposited in the sea, 
the coarser fragments near the shore, the finer particles at 
a distance. Such material is largely clastic and if there have 




Fig. 11. — Block diagram showing how marine soils are formed and their 
relation to the uplands. The emerged coastal plain has already 
suffered some dissection from stream action. (After Emerson.) 

been many changes in shorelines, the alternating beds will 
show no regular sequence. Such material, when raised above 
the sea by diatrophism and subjected to sufficient weathering 
and denudation, is classed as marine soil. (See Fig. 11.) 

Such material has been worn and triturated by a number 
of agencies. First, the forces necessary to throw it into 
stream suspension were active, and next it was swept into 

^ For an excellent discussion of the marine soils of the Atlantic and 
Gulf coasts of the United States see Bennett^ H. H., Soils and Agri- 
culture of the Southern States; New York, 1921. 



GEOLOGICAL CLASSIFICATION OF SOILS 51 

the ocean to be deposited and stratified, possibly after being 
pounded and eroded by the waves for years. At last came 
the emergence above the sea and the action of the forces 
of weathering in situ. The latter effects are of great moment 
since they determine not only the topography but the fertility 
of the new soil as well. The availability of the nutritive ele- 
ments, and especially the amounts of organic matter, are de- 
termined by recent and still active forces. 

The marine soils of the United States, while younger than 
most of our residual soils, are usually more worn and gener- 
ally carry less of the nutrient elements. Their silica con- 
tent is very high and they are often sandy, especially along 
the Atlantic seaboard. Sands, sandy loams, and loams pre- 
dominate, although silt loams and clays are by no means un- 
iisual, especially in the Atlantic and Gulf coastal flatwoods 
and the black prairies and interior flatwoods of Alabama and 
]\Iississippi. The organic content of the sandy soils is gen- 
erally low, but on the heavier types it may almost equal delta 
and flood plain soils. 

A direct comparison ^ between typical coastal plain and 
residual soils usually shows the former to be considerably 
higher in silica but lower in iron and aluminium. The marine 
soil is, on the other hand, lower in phosphoric acid and 
potash. The nitrogen, organic matter, and lime are so vari- 
able in both soils that no reliable deductions can be drawn. 
The following data from Eastern United States substantiate 
the above generalizations.- (Tables VIII and IX, page 52.) 

The soils of the Atlantic and Gulf coastal provinces, formed 
as vast out wash plains and occupying 11 per cent, of the area 
of the United States, are very diversified, due to source of 

^ When soils are compared on the strictly chemical basis great caution 
should be observed in drawing conclusions as to relative productivity. 
The amount of a nutrient present is by no means a measure of its 
availability. A chemical analysis usually throvps but little light on the 
fertilizer needs of a soil. 

*See also Walker, S. S., Chemical Composition of Some Louisiana 
Soils as to Series and Texture; La. Agr. Exp. Sta., Bui. 177, Aug., 1920. 



52 



NATURE AND PROPERTIES OF SOILS 



Table VIII 

COMPARATIVE COMPOSITIONS OF COASTAL PLAIN AND RESIDUAL 
SOILS OF EASTERN UNITED STATES.^ 



Constituents 



SiO^. 
TiO^. 
AI2O3 
Fel^Os 




Residual 



77.72 

.90 

9.13 

3.75 



Table IX 

COMPARATIVE COMPOSITIONS OF NORTH CAROLINA COASTAL PLAIN 
AND RESIDUAL SOILS.^ 



Constituents 


1 
Costal Plain 


2 
Coastal Plain 


3 

Eesidual 


N 


.038 
.027 
.286 
.221 


.138 
.033 
.346 
.394 


.048 


P,0. 


.041 


K,0 


1.330 


CaO 


.200 







^ Robinson, W. O., et ah, Variation in the Chemical Composition of 
Soils; U. S. Dept. Agr., Bui. 551, June, 1917. 

1 and 2. Average analyses of 15 coastal plain anil 8 residual soils, 
respectively, taken from various places in eastern United States. 

^Williams, C. B., et al., Beport on the Coastal Plain Soils; Bui. 
N. C. Dept. of Agr., Vol. 39, No. 50, May, 1918. 

1. Average of 165 analyses of Norfolk series soils. This is 
the typical soil of the Atlantic coastal plain. 

2. Average of 84 analyses of Portsmouth series soils. This 
series isi above the average coastal plain soil in organic 
matter and fertility. 

Williams, C. B., et al., Report on the Piedmont Soils; Bui. N. C. 
Dept. of Agr., Vol. 36, No. 2, Feb., 1915. 

3. Average of 71 analyses of Cecil series soils. This series ia 
the typical residual soil of the Piedmont plateau. 



GEOLOGICAL CLASSIFICATION OP SOILS 53 

material, age, and climatic conditions. There are great 
tracts of general farming land, besides wide areas of special- 
purpose soils adapted to highly specialized industries. The 
latter soils require refined and intensive methods of culti- 
vation. Except for certain areas the coastal plain soils are 
well aerated and easy to cultivate. Except in the lower 
coastal plain belt they are well drained. Severe leaching as 
well as serious erosion occurs in times of heavy rainfall. 
When sufficiently supplied with organic matter, carefully 
fertilized, and cidtivated properly, these soils support a great 
variety of crops such as cotton, maize, oats, forage crops, 
and peanuts, besides vegetables and fruits of many varieties. 
30. The ice age and the American ice sheet. ^ — If in any 
region the temperature and snowfall stand in such rela- 
tionship that the heat of summer does not offset the winter's 
accumulation of snow, great snowfields form. If this con- 
dition persists year after year the temperature is reduced 
to such an extent as to increase the proportion of the snowfall, 
which escapes the summer heat. The pressure of overlying 
snow and the influence of the summer melting soon change 
the snow into ice with a complicated recrystallization. As the 
depth of the accumulation increases outward movement is 
inaugurated due to the strong lateral pressure. As the ice 
moves slowly forward under this tremendous pressure, with 
an almost incredible thickness and a plasticity which ordi- 
nary ice does not possess, it conforms itself to the uneven- 
ness of the areas invaded. It rises over hills and shapes 
itself to valleys with surprising ease. Not only is the exist- 
ing soil mantle swept away by such an invasion but the 
underlying rocks are ground and gouged. When the ice 
melts back and the region is again free a mantle of soil ma- 
terial remains. 

' For a complete discussion of glaciers and glaciation, see Salis- 
bury, E. D., The Glacial Geology of New Jersey; Geol. Survey of 
New Jersey, Vol. 5, 1902. 



54 NATURE AND PROPERTIES OF SOILS 

This drift is often merely ground-up rock, at other times 
the original soil is mixed with foreign detritus, while again 
the variable mixtures may be wholly reworked and consid- 
erably stratified. Besides this the streams of water, which 
issue from under the ice, may be instrumental in distribut- 
ing sediments for miles beyond the ice front. Glacial lakes, 
when in existence for sufficiently long periods, furnish basins 
f6r the deposition of materials derived from the erosive and 
grinding influence of the ice. The ice may also provide a 
large amount of detritus so fine as to be susceptible to wind 
movement, and thus aeolian influences as well as alluvial and 
lacustrine may be concomitant to a great ice invasion. 

During the Pleistocene northern North America, as well 
as part of Europe, was successively invaded by ice sheets, 
which exerted the influences above described and, while the 
central ice caps in Canada probably never wholly disap- 
peared, the regions to the southward certainly experienced 
alternate glaciation and interglaciation. At least five in- 
vasions are evident in central United States. Debris from the 
last, called the Wisconsin, now covers wide areas. The in- 
terglacial periods are shown by forest beds, accumulations 
of organic matter, and evidences of erosion between the drift 
deposited by the successive ice sheets. Some of the inter- 
glacial periods evidently were times of warm, and even semi- 
tropical, climate. Just what was the exact cause of the ice 
age is still under dispute.^ That it was due to a change in 
the carbon dioxide content of the air seems as probable as 
any of the numerous hypotheses that ha\ e been advanced. 

The area covered by glaciers in North America is estimated 
as 4,000,000 square miles, while at least 20 per cent, of the 
United States is either directly or indirectly influenced by the 
debris. The greatest southward extension of the ice is marked 

^ Humphreys, W. J., Factors of Climatic Control, Jour. Franklin Inst., 
Vol. 189, No. 1, pp. 63-98, Jan., 1920. 



GEOLOGICAL CLASSIFICATION OF SOILS 55 

by a terminal moraine wherever the ice margin was station- 
ary long enough to permit such an accumulation. Many 
other moraines are found to the northward, marking points 
where the ice became stationary for a time as it retreated 
by melting.^ While the moraines are generally outstand- 
ing topographic features, they are commonly unimportant 
agriculturally due to their small area and unfavorable physi- 
ography. The ground moraine is the material which fur- 
nishes the bulk of the soils which have directly resulted from 
glaciation. This ground moraine is of wide extent and pos- 
sesses a favorable agricultural topography. The weathering 
in situ of this great area of soil material has evolved one of 
the most productive soil provinces of the world. 

31. Glacial soils. — The soils which have been developed 
from the glacial till are usually rather heavy, loams, silt 
loams, and clay loams predominating. The subsoil is gen- 
erally finer than the surface and may induce poor drainage. 
The individual particles of such soils are less weathered than 
those of residual soils. The feldspars have retained their 
normal luster and the iron staining so common in the Pied- 
mont Plateau is almost absent. The color is usually sub- 
dued, grays and browns prevailing. Red glacial soil may 
occur, however, where red sandstones have been ground up 
or where considerable residual soil has been incorporated 
in the till. The subsoils usually present colors ranging from 
light gray and yellows to brown. Mottling is common, es- 
pecially in the subsoil, due to lack of aeration. 

The chemical composition of glacial soils approaches that 
of the parent rock more nearly than does any other, since 

^ The position of the ice front of a glacier is determined by the 
relationship between the forward movement of the ice and the rate 
of melting. When the former is dominant, the ice front advances. 
When melting in dominant, the ice front recedes. When these two 
forces are balanced, conditions are favorable for a stand of the 
ice and the building of a moraine. 



56 



NATURE AND PROPERTIES OF SOILS 



the forces of weathering, while they have had time to pro- 
duce a soil from the material left by the ice, have not as yet 
seriously depleted the essential constituents. The mineral 
elements in such soils are governed to a considerable degree 
by the composition of the original rock. Calcium content, 




Fig. 12. — Block diagram showing the relationship which sometimes exists 
between glacial soils and the underlying rocks. Glacial movement 
left to right. (After Emerson.) 



for example, is controlled largely by such a relationship. 
The hill soils of southern New York (Volusia and Lords- 
town) come from shales low in lime and their productive- 
ness is seriously affected thereby. On the other hand, cer- 
tain glacial soils of central New York and of the Mississippi 
Valley (Ontario and Miami) have been formed from cal- 
careous till and owe their productivity partly thereto. Gla- 



GEOLOGICAL CLASSIFICATION OF SOILS 57 

cial soils from limestones generally contain plenty of lime, 
a condition that is far from true with residual soils.^ 

The organic content of glacial soils depends to a large 
extent on the climatic conditions under which the soil has 
existed since its formation. If environmental factors have 
been such as to encourage the accumulation of organic mat- 
ter, these soils will exhibit the deep black color that arises 
from the presence of such material. If, however, conditions 
do not encourage the natural growth of a heavy vegetation, 
the amount of organic matter in such virgin soil will be low. 
Lime and other nutritive elements may also be a great factor 
in the development of vegetation on these soils. Glacial till 
soils are distributed over all the area north of the great 
terminal moraine, and stretch, roughly, from New Eng- 
land to the Pacific coast. They comprise a great variety of 
soils, differing not only in their physical characters, but also 
as to fertility. They are adapted to many crops, but general 
farming is practiced on them to the greatest degree. This 
means extensive, rather than intensive, operations. In some 

* Partial Analyses of Soils from the Limestone Driftless and 
Glacial Eegion of Wisconsin'' Are of Interest in This Eegard: 



Constituents 



SiO. 

Al,03 + FeoO 

MgO 

CaO 

K2O 

P.O. 

CO, 



Residual 



71.13 
18.02 
.38 
.85 
1.61 
.02 
.43 



49.13 

31.12 

1.92 

1.22 

1.61 

.04 

.39 



Glacial 



40.22 
11.30 

7.80 
15.65 

2.36 

.05 

18.76 



48.81 
10.07 

7.95 
11.83 

2.60 

.13 

15.47 



^Chamberlain, T. C. and Salisbury, R. D., The Driftless Area of the 
Upper Mississippi; Sixth Ann. Rep. U. S. Geol. Survey, pp. 249-250, 1885. 
These analyses illustrate to very good advantage the beliefs entertained 
by Chamberlain and Salisbury regarding the differences between residual 
and glacial clays. Residual clay is designated by them as * * rock rot, ' ' 
and glacial clay as ' ' rock flour, ' ' The latter, being less weathered, "re- 
tains a larger proportion of its easily soluble materials. 



58 NATURE AND PROPERTIES OF SOILS 

regions dairying has been developed to a large extent, while 
in certain localities, where climate, soil, and market are fa- 
vorable, trucking is of great importance. 

32. Effect of glaciation on agriculture.^ — In comparing 
glaciated soils with corresponding residual areas, certain 
differences are usually apparent. The agi-icultural condition 
within the zone of glaciation is usually consistently higher 
than that beyond the regions of drift accumulation. The 
extensive leveling due to glacial erosion and deposition has 
almost always resulted favorably for agricultural operations. 
Even the thickness of the drift is found to conserve the 
ground water supply. While it is difficult to show any con- 
sistent difference between residual and glacial soils as to total 
constituents, it is generally admitted that glaciation has been 
a benefit to agriculture, in that the soils have been rejuven- 
ated and their crop-producing power raised. 

The dominant textural quality of glacial soils seems adapted 
to certain staple food crops, and, due to their interming- 
ling, a considerable opportunity for diversified and intensi- 
fied farming is offered. It is, therefore, evident that in any 
study of soils, particularly those of the United States, a 
careful consideration of the effects of glaciation is neces- 
sary. Even the alterations in topography are factors not 
to be ignored. In a comparison of the driftless area of Wis- 
consin with the glaciated parts only 43 per cent, of the 
former is improved as against 61 per cent, of the latter, while 
the value of the farms on the glaciated soil averages 50 per 
cent higher. The same general differences appear between 
the glacial and residual soils of Indiana and Ohio. 

33. Lacustrine soils — glacial lake. — Great torrents of 
water were constantly gushing from the front of the great 

^ Whitbeck, E. H., The Glaciated and Driftless Portions of Wisconsin; 
Bui. Geog. Soe. Phil., Vol. IX, No. 3, pp. 10-20, 1911. Von Englen, 
O. D., Effects of Continental Glaciation on Agriculture; Bui. Amer. 
Geog. Soc, Vol. XLVI, pp. 353-355, 1914. Ames, J. W., and Gaither, 
E. W., Soil Investigations; Ohio Agr. Exp. Sta., Bui. 261, 1913. 



GEOLOGICAL CLASSIFICATION OF SOILS 59 

ice sheets as they advanced and retreated in response to their 
environment. The great loads of sediment carried by such 
streams were either dumped down immediately or carried to 
other areas for deposition. As long as the water had ready 
egress it flowed rapidly away to deposit its load as gravelly 




Fig. 13. — Diagram showing how glacial lakes were formed in New York 
State. The lighter shading represents the Ontarian ice lobe; the 
darker shading indicates the position of the glacial lake waters in 
the Ontario and Hudson river basins. (After Fairchild.) 



outwash, river terraces, valley trains and alluvial fans. In 
many cases, however, the ice front came to a stand where 
there was no such ready egress and ponding occurred. Often 
very large lakes were formed which existed for many years. 
(See Fig. 13.) 

With the ice melting rapidly on the hill tops these lakes 
were constantly fed by torrents from above, which were 
laden with sediment derived not only from under the ice, 



60 NATURE AND PROPERTIES OF SOILS 

but also from the unconsolidated till sheet over which it 
flowed. As a consequence there were in the glacial lakes 
deposits ranging from coarse delta materials near the shore to 
fine silts and clay in the deeper and stiller waters. Such 
materials now cover large areas, not only in New York state 
and along the Great Lakes, but also in the Red River Valley 
and in the valleys of the Rocky Mountains and the Cascades 
and Sierra Nevadas. They make up by far the most im- 
portant of the lacustrine soils. Glacial lake soils probably 
present as wide a variation in physical characteristics as any 
of the great soil provinces. Being deposited by water they 
have been subject to much sorting and stratification, and 
range from coarse gravels on the one hand to fine clays 
on the other. They are generally found as the lowland soils 
in any region, although they may occur well up on the 
hillsides if the shores of the old lakes encroached thus far. 
The color of such soils varies from gray to black, according 
to the degree of organic matter present. The organic con- 
tent of such soils, as with the glacial till, varies with climate, 
and may be high, low, or medium according to conditions. 
The thickness of glacial lake deposits is variable, ranging 
from a few to many feet. In chemical composition they 
closely approximate the soil material from which they were 
derived. This is particularly true as regards the presence 
of lime. The distribution of glacial lake deposits is not 
only wide but the areas are large enough to be of great 
agricultural influence. Extending westward from New 
England along the Great Lakes until the broad expanse 
of the Red River Valley is reached these deposits have pro- 
duced some of the most important soils of the northern 
states. They are valuable not only for extensive cropping 
with grain and hay, but also for fruit and trucking. 

34. Lacustrine soils — ^recent lake. — While the glacial 
lake deposits were formed many thousands of years ago the 
lake soils of the second group are still in process of construe- 



GEOLOGICAL CLASSIFICATION OF SOILS 61 

tion. It is a well-known fact that lakes are only enlarged 
stream beds, and are doomed ultimately to be filled by river 
sediments. Such soils have been reclaimed to a certain ex- 
tent, but their acreage is not large enough to give them the 
importance of the glacial lake soils. The lake soil is usually 
of a fine character, rich in organic matter and of good tilth. 
If properly drained, it is almost invariably highly produc- 
tive, and is adapted to a variety of crops depending on cli- 
matic conditions. 

35. .^olian soils. — Loess. — During glaciation much fine 
material was carried miles below the front of the ice sheets 
by streams that found their source within the glaciers. This 
fine sediment was deposited over wide areas by the over- 
loaded rivers. The accumulations occurred below the ice 
front at all points, but seem to have reached their greatest 
development in what is now the Missouri Valley and the 
Great Plains. Much of the sediment in the latter area prob- 
ably came from local glaciers, which debouched from the 
Rockies. 

It is generally agreed by glacialists, that a period of aridity, 
at least as far as this particular region is concerned, im- 
mediately followed the retreat of the ice. The low rain- 
fall of this period was accompanied by strong westerly winds. 
These winds, active perhaps through centuries, were instru- 
mental in the picking-up and distributing of this fine ma- 
terial over wide areas of the Mississippi, Ohio, and Missouri 
valleys. One strong argument for this asolian origin is that 
the soil is in its deepest and most characteristic development 
along the eastern banks of the large streams. Especially 
noticeable is the extension down the eastern side of the Missis- 
sippi River almost to the Gulf of Mexico. This wind-blown 
material, called loess, is found over wide areas in the United 
States, in most cases covering the original till mantle. It 
covers eastern Nebraska and Kansas, southern and central 
Iowa and Illinois, northern Missouri and parts of Ohio and 



62 NATURE AND PROPERTIES OF SOILS 

Indiana, besides a wide band, as already noted, extending 
southward along the eastern border of the Mississippi River. 
Due to its mode of origin, its depth is always greatest near 
the streams and gradually becomes less farther inland. In 
places, notably along the Missouri and Mississippi rivers, its 
accumulation has given rise to great bluffs, which bestow a 
characteristic topography to the region. 

Not only is loess found over thousands of square miles in 
the central part of the United States but it occurs else- 
where in large areas. It is greatly developed in northern 
Prance and Belgium, and along the Rhine in Germany, where 
it is an important soil in all the valleys that are tributary 
to that river. Silesia, Poland, southern Russia, Bohemia, 
Hungary and Roumania have deposits of this highly fertile 
material. Some of the most important moves of the World 
War had as their aim the possession of these fertile areas. 
In China loess is found over a very large part of the valley 
of the Hwangho, a region probably larger in area than Prance 
and Germany combined. The thickness of the deposit is 
variable, ranging from a few feet to several thousand in 
places. The depth is practically always sufficient for any 
form of agricultural operations. 

Loess is usually a fine calcareous silt or clay loam, of a 
yellowish or yellowishy buff color. While it may be readily 
pulverized when subjected to cultivation, it possesses remark- 
able tenacity in resisting ordinary weathering. The vertical 
walls and escarpments formed by this soil show one of its 
striking physical characteristics. In China caves that house 
thousands of persons are dug in the defiles and canons ex- 
isting in this deposit. Another feature of loess is the pres- 
ence, especially in the subsoil, of minute vertical canals lined 
with a deposit of calcium carbonate. These canals are sup- 
posed to give the soil its vertical cleavage and its tenacity. 
The particles of loess are usually unweathered and angular. 
Quartz seems to predominate, but large quantities of feld- 



GEOLOGICAL CLASSIFICATION OF SOILS 63 



spar, mica, hornblende, augite, caleite and other minerals 
are found. 

A few typical analyses are given below which show the 
variability that may be expected, especially in the nitrogen, 
phosphoric acid, potash, and lime. 

Table X 

ANALYSES OF AMERICAN LOESS SURFACE SOILS^ 



Constituents 


1 


2 


3 


4 


SiOo 


71.30 
.60 


81.13 

.78 


86.96 
.69 


69.66 


TiOo 


1.72 


AUO3 


11.47 


8.52 


4.69 


12.71 


FeA 


4.05 


2.92 


2.86 


4.89 


MgO 


1.10 


.39 


.43 


1.28 


CaO 


1.38 


.31 


.71 


1.09 


Na.O 


1.95 


.52 


1.07 


1.17 


K,0 


2.40 


1.78 


.91 


2.42 


PA 


.23 


.08 


.07 


.15 


N 


.22 


.11 


.11 


.23 







Whenever moisture relations are favorable, loess is an 
exceedingly fertile soil. Under heavy cropping, especially 
when little in the way of organic or mineral matter is re- 
turned, this soil shows a need of phosphoric acid and lime, 
the application of which is becoming part of good farm prac- 
tice in the Central West. Considering the wide extension of 

^ 1. Marshall silt loam, Pottawattamie Co., la. 

Bennett, H. H., Soils and Agriculture of the Southern States, 
p. 332; New York, 1921. 

2. Memphis silt loam, Grenada Co., Miss. 

Eobinson, W. O., et al.. Variation in the Chemical Composition 
of Soils; U. S. Dept. Agr., Bui. 551, June, 1917. 

3. Cherokee silt loam, Cherokee Co., Kan. 

Bennett, H. H., Soils arid Agriculture of the Southern States, 
p. 332; New York, 1921. 

4. Silt loam, Weeping Water, Neb. 

Alway, F. J., and Eost, C. O., The Loess Soils of the NehrasTca 
Portion of the Transition Begion, Part IV; Soil Sci., Vol. I, 
No. 5, p. 431, May 1916. 



64 NATURE AND PROPERTIES OF SOILS 

the loess and the great variety of climate and cropping to 
which it is subject, it may be classed as one of the world's 
most important soils. In the United States it is the great 
maize-producing soil of the upper Mississippi Valley. 

36. Other seolian soils. — The term ' ' adobe ' ' is applied to a 
fine calcareous clay or silt formed in a manner somewhat 
like loess. It is supposed that, while part of the deposit came 
from the waste of talus slopes as mountains were weathered 
under conditions of aridity, the remainder had aiolian origin. 
Certain characteristics also seem to indicate that the valley 
adobe might have been deposited almost entirely by water. 
It appears, therefore, that, while the physical characteristics 
of all adobe are somewhat similar, its mode of origin and 
chemical composition may be variable. 

Like the loess, the adobe is an exceedingly rich soil, but 
it occurs in an arid or a semi-arid region. When irrigated 
its fertility seems inexhaustible. It is found in Colorado, 
Utah, southern California, Arizona, New Mexico, and Texas. 
It has an especially wide distribution in New Mexico. Like 
loess, its elevation is variable, ranging from sea level in Cali- 
fornia and Arizona to 6000 feet along the eastern border of 
the Rocky Mountains. Its maximum thickness cannot be esti- 
mated, as it is very little eroded and is supposed to be still 
accumulating. Some valleys are known to be filled to a depth 
of 3000 feet with this material. Its characteristics are its 
fine texture, its great depth, its wide distribution, and its 
great fertility when moisture conditions are suitable for crop 
growth. 

Sand dunes are the outgrowth of two conditions — a large 
quantity of sand and a wind that blows in a more or less 
prevailing direction. Under such conditions the sand and 
other fine materials are not only blown into heaps, but also 
tend to move in the direction of the prevailing wind. Sand 
dunes may often assume gigantic proportions, sometimes be- 
ing several hundred feet high and twenty or thirty miles 



GEOLOGICAL CLASSIFICATION OF SOILS 65 

long. In such proportions they become a grave menace to 
agriculture, not only because they are an absolutely valueless 
medium for plant growth, but also because they cover fertile 
lands and entirely blot out all vegetation. 

From early geologic times deposits of the very fine material, 
that is continually being ejected from volcanoes, have been 
distributed over the earth's surface. These deposits are 
usually flour-like, and while at one time they probably cov- 
ered many square miles of territory, they have succumbed 
very largely to erosion and denudation, and only remnants 
are found at the present time. Such material may be found 
in Montana, Nebraska, and Kansas, ^olian deposits of this 
character are usually rather porous and light, and are likely 
to be highly siliceous. They are not of great agricultural 
importance, except in certain localities. 

37. Resume. — The geological classification of soils pro- 
vides a logical basis for the discussion of the formation, char- 
acter, and agricultural value of soils in general. A detailed 
consideration on any other basis would lead to endless con- 
fusion and repetition. In classifying soils a study must be 
made not only of the past effects but of the present influences 
of the soil-forming processes, and while the conclusions and 
observations are apparently purely agricultural in nature, 
they really spring from a geochemical foundation. 

With such a classification at hand one cannot fail to under- 
stand the occurrence of so many distinct and dififerent types 
of soil. It is really difficult to see why soils do not present 
greater differences and why transition types do not utterly 
prevent clean-cut field distinctions. In such soil study the 
all-important character of climatic control must always be 
remembered. Weathering is strictly a climatic influence and 
crop adaptation is usually dominated by climate rather than 
by soil. 



CHAPTER IV 

THE SOIL PARTICLE AND CERTAIN IMPORTANT 
RELATIONS 

An examination of a soil, however cursory, immediately 
reveals that it is made up of irregular fragments of mineral 
material mixed and more or less coated with organic matter. 
These fragments, varying in size from particles easily discern- 
ible by the naked eye to particles so fine as to be invisible 
under the ultra-microscope, determine to a very large degree 
the complex relationships of soil to plant. The movement of 
air in the soil, the circulation of the water, chemical reactions 
resulting in solution, and the presence and virility of the 
various organisms are determined largely by the size of par- 
ticles making up a soil and by the proportion and condition 
of the organic material present. In expressing the size or 
sizes of particles making up a soil, the term texture is used. 
Thus a soil texture may be coarse, medium, or fine, indicating 
that the particles making up the soil conform in general to 
such description. 

Texture is a condition which can be but little modified in 
a normal soil. We have seen how a rock can be disintegrated, 
decomposed and gradually built into a soil. A change in 
texture has been Avrought, but such a process demands geo- 
logic ages for its fulfillment. In the time covered by the life 
of man, the necessary forces are not active enough to have 
this effect ; consequently, as far as the farmer is concerned, 
the texture of the soil in his field is subject to but slight 
alteration. A sand remains a sand and a claj' remains a clay, 
as far as practical considerations are concerned. Changes 

66 



THE SOIL PARTICLE 



67 



in texture may be made on a small scale by mixing two soils, 
but this is not practicable in the field. 

38. Separation and classification of soil particles. — In 
order that the particles of soil, varying so tremendously in 
size as they do, may be studied successfully, they must be 
separated into groups according to their diameters. The va- 
rious groups are spoken of as soil separates. Such a grouping 
is of course arbitrary, and must meet certain theoretical as 
well as practical requirements. It must be simple, short, and 
capable of expressing in a practical way the physical char- 
acter of the soil. Moreover, it must lend itself to the actual 
separation and percentage evaluation of each group. This 
analytical procedure is called a mechanical analysis. 

With the large number of different methods of mechanical 
soil analyses, there has arisen considerable variation in tex- 
tural groupings expressed in diameter of particles. This 
would naturally occur because of the differences in degree of 
refinement, which the various methods of separation allow, 
and also because of the uses which the investigators wished to 



Table XI 

THE NAMES AND RANGES IN SIZE OF SOIL PARTICLES AS ESTAB- 
LISHED BY THE BUREAU OF SOILS CLASSIFICATION^ 



Separate 


Size in 
Millimeters 


Fine Sandy 
Loam 


Clay 


1. Fine Gravel. . .. 

2. Coarse Sand . . . 

3. Medium Sand . . 

4. Fine Sand 

5. Verv Fine Sand 

6. Silt' 


m.m. 
2—1 
1— .5 
.5— .25 
.25— .10 
.10— .05 
.05— .005 
.005 and below 


% 

1 

2 

3 

22 

35 

27 

10 


% 
1 
2 
2 
6 
7 

39 


7. Clay 


43 







^ Briggs, L. J., et ah, The Centrifugal Method of Soil Analysis; U. S. 
Dept. Agr., Bur. Soils, Bui. 24, 1904. 



68 



NATURE AND PROPERTIES OF SOILS 



make of such analyses. The grouping established by the 
United States Bureau of Soils is met with in all soil literature 
and is really the standard classification for this country. 
Table XI sets forth the essential points of the Bureau of Soils 
classification. In the first column are given the names of the 
various separates, and in the second the range in size of each 
group. Columns three and four show the percentages of each 
separate in two very different specimen soils, a sandy loam 
and a clay. In order to obtain such figures, a sample of the 
dry soil must actually be separated into the arbitrary groups 
and the percentage of each group to the whole soil calculated 
from the dry weights obtained. This operation is the mechan- 
ical analysis already mentioned. 

This classification establishes seven distinct groups^ rang- 



^ Various Teixtueal. Classifications Other Than That of 
Bureau of Soils Used in the Mechanical Analyses 
of Soils. Expressed in Diameter op Par- 
ticles IN Millimeters 



Separate 


Osborne* 


Hilgard' 


English* 


Atterberg* 


1 


3.00-1.00 


3.00-1.00 


1.00 - .200 


20.00 -2.00 


2 


1.00- .50 


1.00- .50 


.20 - .040 


2.00 - .20 


3 


.50- .25 


.50- .30 


.04 - .010 


.20 - .02 


4 


.25- .05 


.30- .16 


.01 - .002 


.02 - .002 


5 


.05- .01 


.16- .12 


.002 


.002- — 


6 


.01- — 


.12- .07 

and six 

other divisions 







* Osborne, T. B., Methods of Mechanical Soil Analysis; Ann. Eep. 
Conn. Agr. Exp. Sta., 1886, pp. 141-158; 1887, pp. 144-162; 1888, pp. 
154-157. 

^ Ililgard, E. W., Methods of Physical and Chemical Soil Analysis; 
Ann. Eep. Cal. Agr. Exp. Sta., 1891-1892, pp. 241-257. 

=■ Hall, A. D. and Eussell, E. J., Soil Surveys and Soil Analysis; Jour. 
Agr. Science, Vol. IV, part 2, pp. 182-223, 1911. 

* Atterberg, A., Die Mechanische Bodenanalyse und die Klassifikation 
der Mincralboden Schwedens. Internat. Mitt. f. Bodenkunde, Band II, 
Heft 4, Seite 312-342, 1912. Schucht, P., tJber die Sitzung der Inter- 
nationalen Kommission fur die Mechanische und Physikalische Boden- 
untersuchung in Berlin am 31, October 1913; Internat. Mitt. f. Boden- 
kunde, Band IV, Heft I, Seite 1-31, 1914. 



THE SOIL PARTICLE 69 

ing from fine gravel, readily visible to the naked eye, to the 
clay separate, the largest particle of which is ,005 of a milli- 
meter or .0002 of an inch in diameter. The stone and large 
gravel, while they figure in a practical examination and de- 
scription of a soil in the field, obviously need not be considered 
in such a classification as this. 

The seven separates may be thrown into two groups for 
a preliminary examination on the basis of visibility to the 
naked eye. The gravel and sand particles are readily seen, 
while the silt and especially the clay particles are invisible 
as individuals, although some of the larger silt particles may 
be seen with the naked eye when suspended in water. The 
gravel and sand, when dominant in a soil, give properties 
known to every one as sandy, while if the soil is made up 
largely of silt and clay, its plasticity and stickiness proclaim it 
as clayey in nature. The characteristics of the two soils of the 
above table may be read easily from their mechanical analyses. 
The classification, therefore, meets the criteria already estab- 
lished. It is simple, easy to remember, and is capable of 
expressing, to a certain extent at least, the dominant physical 
characters of soils. As will be shown below, it lends itself 
to the quantitative separation of a soil, the so-called mechan- 
ical analysis. 

39. The beaker method of mechanical analysis. — When 
fragments of rock or soil are suspended in water they tend 
to sink slowly, and it is a well recognized fact that, other 
things being equal, the rate of settling depends on the size 
of the particle. As the particle is decreased in size its weight 
decreases faster than the surface exposed to the buoyant force 
of the water. As a consequence the rapidity with which the 
soil particles settle is more or less proportional to their size. 
The suspension of a sample of soil would, therefore, be the 
first step in mechanical separation by water; the second step 
would be subsidence and the withdrawal of each successive 
grade of particles as it slowly settled; the third step would 



70 NATURE AND PROPERTIES OF SOILS 

be the determination of the percentage of each grade, or group, 
of particles as based on the original sample. This is precisely 
what every method of mechanical analysis in which water is 
utilized aims to do, although the irregularity in the shape of 
the particles prevents to a certain extent a perfect separa- 
tion. The apparatus and technique of the various methods 
employed are generally rather complicated. 

One of the earliest and most useful methods to be perfected 
was the separation of the various grades of soil by simple 
subsidence in a column of still water. This is commonly 
spoken of as the Osborne beaker method.^ The determination 
is very simple. The soil sample is first fully deflocculated and 
thrown into suspension, each particle functioning separately. 
Beakers are commonly used as containers, but any vessel that 
is relatively deep will do for the determination. The larger 
particles, gravel and sand, will of course settle first, and the 
finer silts and clays may be decanted off. As the sands carry 
finer particles down with them, the suspension and subsidence 
must be repeated a number of times. The sands are later 
dried and sieved into their respective groups. The silt and 
clay particles, thus decanted, may be separated from each 
other by subsidence as above described. The time necessary 
for such decantation as will leave in suspension only particles 
below a given size is determined by the examination of a drop 
of the suspension under a microscope fitted with an eyepiece 
micrometer. In this way the size of the particles decanted 
may be measured accurately. (See Fig. 14.) 

The four steps in this method of separation are : defloccula- 
tion of the sample ; separation by successive subsidence and 
decantation ; evaporation to dryness of the separates and the 
sieving of the sands; and the weighing of the separates and 
the calculation of percentages based on the original dry sam- 

* Osborne, T. B., Methods of Mechanical Soil Analysis; Ann. Rep. 
Conn. Agr. Exp. Sta., 1886, pp. 141-158; 1887, pp. 144-162; 1888, pp. 
154-157. 



THE SOIL PARTICLE 



71 



pie. The method, however, is slow, as the time necessary for 
each subsidence of the finer particles is very great and the 
number of individual subsidences is large. As a consequence, 
it has been superseded by methods that utilize centrifugal 
force for the finer separations, while retaining gravity for 
removing the various grades of sand. 




Fig. 14. — Diagram showing the relative sizes of soil particles as they 
appear under a microscope with eye-piece micrometer. Particles 
one space or less in diameter are clay; from one space to ten, silt 
and above ten spaces, very fine sand. 



40. Bureau of Soils centrifug'al analysis. — Of the cen- 
trifugal methods used in mechanical analysis that employed 
by the United States Bureau of Soils^ is the most successful. 
A five-gram sample of well-pulverized soil is put into a shaker 
bottle of about 250 cubic centimeters capacity. This bottle 
is filled about two-thirds full of water so that in shaking the 
disintegrating force of the liquid may be utilized. A few 

^Fletcher, C. C. and Bryan, H., Modifications of the Method of Soil 
Analysis; U. S. Dept. Agr., Bur. Soils, Bui. 84, 1912. 



72 NATURE AND PROPERTIES OF SOILS 

drops of ammonia are added to dissolve the organic matter 
and to make deflocculation easier. Tiie sample is then agi- 
tated in the bottle until disintegration is complete. This 
period ranges from five to twenty hours, depending on the 
sample. (See Fig. 15.) 

The separation of the silt and the clay from the sands is 
made in the shaker bottle by simple subsidence, the time for 
decantation being determined by a microscopic examination 
of a drop of the suspension. The silt and the clay are de- 
canted directly into a test-tube fitted into a centrifuge. Whirl- 
ing at the rate of 800 to 1000 revolutions a minute -will cause 
the subsidence of the silt to the bottom of the test-tube in a 
few minutes. The clay is then decanted. The microscope is 
necessary here in order to determine when the settling of the 
silt is complete. As small particles tend to cling to the larger 
particles the entire operation must be repeated several times; 
therefore the processes of gravity subsidence and centrifugal 
subsidence are carried on side by side, material being con- 
stantly poured from the shaker bottle into the centrifuge tubes 
and from the test-tubes into the receptacles for the clay. 

The centrifuge is usually large enough to allow the separa- 
tion of several duplicate samples at once. The various sep- 
arates made by this method are dried and weighed. The 
sands, which are obtained in bulk, are further separated by 
sieves into the grades desired. When a large quantity of 
organic matter is present it must be determined and included 
in the final report on the sample. 

This method of mechanical analysis as perfected by the 
Bureau of Soils has been very commonly adopted by soil work- 
ers. It has many advantages over other methods.^ In the 
first place, it is rapid, often requiring only hours where other 



^ Classification of the Various Methods of Mechanical Analysis 

d to sepa: 
methods. 



r Wet 
^ o- ! Used to separate sands in practically all 



[Dry 



THE SOIL PARTICLE 73 

methods take days for completion ; secondly, it is simple, and 
the technique of the separation is easily acquired ; thirdly, in 
the decantations no very large amount of water is accumulated 
with the separates, except for the clay, and thus the time and 
cost of evaporation is reduced. The clay, moreover, may be 
as accurately determined by difference as by direct methods, 
thus allowing a further saving of time. While the method 
is accurate only within one per cent., it is sufficiently precise 
for all practical purposes. 

41. Physical characters of the soil separates. — It is im- 
mediately apparent that as these groups vary in size they 
must exhibit properties, especially physical ones, which are 
widely different. These properties should in turn be imparted 
to the soil of which the separates form a part. If a person is 

2. Air (Cushman's^ air elutriator). 

[Gravity (Schone's' elutriator 
I and Hilgard 's ^ churn elutria- 
In motion ■( tor). 

Centrifugal (Yoder's * Centrifu- 
gal elutriator). 
■ Gravity (Osborne's beaker 
method and Atterberg's" modi- 
At rest < fied silt cylinder). 

Centrifugal (Bureau of Soils 
method). 

For a detailed discussion of all methods of mechanical analysis see 
Wiley, H. W., Agricultural Analysis, Vol. I, pp. 195-276; Easton, Pa,, 
1906. 

* Cushman, A. S. and Hubbard, P., Air Elutriation of Fine Poivders; 
Jour. Amer. Chem. Soc, Vol. 29, No. 4, pp. 589-597, 1907. 

^Schone, E., tJber Schldmmansalyse ; Bui. Soc. Imperiale des Natural- 
istes de Moscow, 40, Part 1, p. 324, 1867. tJber Schldmmanalyse und 
einen neuen Schldmmapparat ; Berlin, 1867. Also see Wiley, H. W., 
Agricultural Analysis, Vol. I, pp. 231-241; Easton, Pa., 1906. 

'Hilgard, E. W., Methods of Physical and Chemical Soil Analysis; 
Ann. Rep. Calif. Agr. P^xp. Sta., pp. 241-257, 1891-1892. 

*Yoder, P. A., A New Centrifugal Soil Elutriator; Utah Agr. Exp. 
Sta., Bui. 89, 1904. 

' Appiani, G., Tiber einen Schldmmapparat fur die Analyse der Boden- 
und Thonarten; Forsch. a.d. Gebiete d. Agri-Physik, Band 17, Seite 291- 
297, 1894. Atterberg, A., Die Mechanische Bodenanalyse und die Klassi- 
fikation der Mineralboden Schwedens ; Internat. Mitt. f. Bodenkunde, 
Band II, Heft 4, Seite 312-342, 1912. 



Water ' 



74 



NATURE AND PROPERTIES OF SOILS 



conversant with these various values, a mechanical analysis 
should reveal at a glance certain soil conditions, which may 
or may not be conductive to the best plant growth. 

The sands and the gravel, because of their sizes, function 
as separate particles. They are irregular and rounded, the 
continual rubbing tliat they have received being sufficient in 

many cases to have ef- 
faced their angular char- 
acter. They exhibit very 
low plasticity and cohe- 
sion, and as a consequence 
are little influenced by 
changes in water content. 
Their water-holding ca- 
pacity is low, and because 
of the large size of the 
spaces between each sep- 
arate particle the passage 
of percolating water is 
rapid. They, therefore, 
facilitate drainage and 
encourage good air move- 
ment. In all the grades 
of sand, the separate par- 
ticles are visible to the 
naked eye, a condition 
impossible with the silt 
and clay groups. Soil containing much sand or gravel, there- 
fore, is of open character, possessing good drainage and 
aeration, and is usually in a loose friable condition. 

The clay and silt particles are very minute, many of the 
former being so small as to be invisible under the ultra-micro- 
scope. Both groups are really shreds and fragments of min- 
erals often rather gelatinous in nature. The clay particles 
are highly plastic and when kneaded with just the correct 




Fig. 15. — Apparatus for making a 
mechanical analysis of soils. 
Shaker -bottle (A), shaking-rack (B) , 
sieves (C), centrifuge (D) and cen- 
trifuge-tube (E). 



THE SOIL PARTICLE 75 

amount of water tliey bccouie sticky and impervious. On dry- 
ing, they shrink with the absorption of considerable heat. On 
wetting, again swelling occurs. The absorptive capacity of 
clay material for water, gases, and soluble salts is very high, 
due to the presence of colloidal material.^ As material in a 
colloidal condition is very finely divided, it is found largely 
in the heavier types of soil. Some clays carry very large 
amounts of material in a colloidal state. Silt possesses the 
same properties of plasticity, cohesion, and absorption as does 
clay, but to a less extent, because the particles of the former 
are larger than those of the latter. The presence of silt and 
especially clay in soil imparts to it a heavy texture, with a 
tendency to slow water and air movement. Such a soil is 
highly plastic, but becomes sticky when too wet, and hard 
and cloddy when too dry. The expansion and the contraction 
on wetting and drying are very great. The water-holding 
capacity of a clayey or silty soil is high. Such soils are spoken 
of as heavy because of their working qualities in the field in 
contrast to the easily tilled sandy soils. 

42. The mineralogical and chemical characteristics of 
soil separates. — From the mineralogical standpoint there 
are often considerable differences between the soil separates, 
especially when the sands and clays are compared. Quartz 
would naturally be expected to persist and because of its low 
solubility would very soon be dominant not only in the coarser 
separates but in the silt and clay as well. Other minerals, 
such as the feldspars, hornblende, mica, and augite being less 
resistant would concentrate in the finer separates. This tend- 

^ The colloidal state — when material is in a very fine state of division, 
approaching but not attaining a molecular condition (true solution), it 
assumes certain characteristic properties, such as high absorption for 
water, gases, and salts in.solution. It may also, under certain conditions, 
cause a marked increase in plasticity and cohesion. The colloidal con- 
dition is purely physical and depends on fineness of division, the 
particles being molecular complexes. Material in a colloid state is 
heterogeneous and is dispersed through a second material called the 
dispersive medium. 



76 



NATURE AND PROPERTIES OF SOILS 



ency together with the formation, as weathering proceeds, 
of the fine coloidal-like epidote, chlorite and similar groups, 
should in general keep the percentage of minerals other than 
quartz higher in the finer portions of a soil.^ The following 
data sustain this assumption: 

Table XII 

MINERALS OTHER THAN QUARTZ IN THE SANDS AND SILTS OP 
VARIOUS SOILS - 



Soils 


Minerals Other Than Quartz in 




Sands 


Silts 


12 Residual 


15% 
12 
5 
37 


21% 

15 

18 


6 Glacial and Loessial 
4 Marine 


3 Arid 


42 







It is to be seen immediately that in every case the silt car- 
ries a large quantity of the important soil-forming minerals 
and a smaller amount of quartz than does the sand. This re- 
veals at least one of the reasons for the greater fertility and 
lasting qualities of fine-textured soils as far as agricultural 
operations are concerned. It is important to note, however, 

^ A petrographic analysis as now developed is very unsatisfactory as it 
throws practically no light on the character of the clay group because 
of the extreme fineness of this material. Even for silt the results are 
unsatisfactory and difficult to express quantitatively. The correlation 
of a petrographic analysis and productivity is vague. 

^ McCaughey, W. G., and Fry, W. H., The Microscopic Determina- 
tion of Soil-forming Minerals; U. S. Dept. Agr., Bur. of Soils, Bui. 91, 
1913. See also, Plummer, J. 'K., Belation of the Mineralogical and 
Chemical Composition to the Fertility Requirements of North Carolina 
Soils; N. C. Agr. Exp. Sta., Tech. Bui. 9, 1914. Plummer, J. K., 
Petrography of Some North Carolina Soils and its Relationship to their 
Fertiliser Requirements ; Jour. Agr. Res., Vol. V, No. 13, pp. 569-581, 
1915. Eohinson, W. O., The Inorganic Composition of Some Important 
American Soils; U. S. Dept. Agr.," Bui. 122, Aug., 1914. Shorey, F. C, 
et al., Calcium, Compounds in Soils; Jour. Agr. Res., Vol. VII, No. 3, 
pp. 57-77. Jan., 1917. 



THE SOIL PARTICLE 77 

that, although quartz is the predominating mineral in sands, 
all the common soil-forming minerals are usually accessory.^ 

It is interesting in passing to observe the differences ex- 
hibited by the various soil provinces although the number of 
samples shown by Table XII are far too small for definite 
conclusions. The marine soils are particularly low compared 
with the residual and glacial, due to the hard usage which 
the soil material of the former has received. No significant 
differences exist between the glacial and residual soils. The 
arid soils, however, are markedly higher in the important min- 
erals due to the suppression of chemical weathering and the 
activity of the physical agents. The silica in such soils is 
held as complex silicates, which carry the elements that are 
so important in plant development. Although these data are 
based on but a few samples, they are so concordant with what 
would naturally be expected that these general conclusions 
cannot be avoided. 

The mineralogical examination has revealed a larger per- 
centage of such minerals as feldspars, mica, hornblende, and 
the like, in the finer separates. A larger percentage of the 
important nutrient elements would, therefore, be expected in 
those groups. The following data,^ compiled from work per- 
formed by the United States Bureau of Soils, substantiate this 
assumption. (See Table XIII, page 78.) 

It is evident that the finer portions of soil are in general 

* Below is given the mineralogical description of a loessial silt loam of 
the Marshall Series from Missouri: Robinson, W. O., The Inorganic 
Composition of Some Important American Soils; U. S. Dept. Agr., Bui. 
122, Aug., 1914. 

Very fine sand — minerals other than quartz, 20 per cent. Orthoclase, 
10 per cent. Muscovite, 2 per cent. Biotite, magnetite, epidote, albite, 
labradorite, oligoclase, tourmaline, zircon, garnet, and augite are also 
present. 

Silt — Minerals other than quartz, 34 per cent. Orthoclase, 4 per cent. 
Muscovite, 4 per cent. Biotite, magnetite, epidote, albite, labradorite, 
oligoclase, tourmaline, rutile, glaucophane, hornblende, and augite are 
also present. 

* Failyer, G. H., and Others, The Mineral Composition of Soil Particles; 
U. S. Dept. Agr., Bur. Soils, Bui. 54, 1908, 



78 



NATURE AND PROPERTIES OP SOILS 



Table XIII 

CHEMICAL COMPOSITION OF VARIOUS SOIL SEPARATES 





Num- 


Percentage of 


Percentage of 


Percentage of 


Soils 


ber OF 

Sam- 


P^O, IN 


K„OiN 


CaOiN 




ples. 


Sand 


Silt 


Clay 


Sand 


Silt 


Clay 


Sand 


. Silt 


Clay 


Crystalline 






















Residual . . . 


o 


.07 


.22 


.70 


1.60 


2.37 


2.86 


.50 


.82 


.94 


Limestone 






















Residual . . . 


3 


.28 


.23 


.37 


1.46 


1.83 


2.62 


12.26 


10.96 


9.92 


Coastal Plain. 


7 


.03 


.10 


.34 


.37 


1.33 


1.62 


.07 


.19 


.55 


Glacial and 






















Loessial . . . 


10 


.15 


.23 


.86 


1.72 


2.30 


3.07 


1.28 


1.30 


2.69 


Arid 


2 


.19 


.24 


•45 


3.05 


4.15 


5,06 


4.09 


9.22 


8.03 



richer in phosphoric acid, potash and lime than the coarser. 
As would be expected the sands, silts, and clays of arid soils 
show less difference than those of the other provinces. Under 
arid conditions the sands have not as yet become depleted of 
their store of essential elements. Average figures compiled 
from Hall 's analyses ^ of soils from southeastern England cor- 
roborate the data already noted. In addition. Hall shows that 
the magnesia, iron, and alumina are higher in the finer sep- 
arates while there is considerably more silica in the sand 
groups,^ 

*Hall, A. D., and Russell^ E. J., Soil Surveys and Soil Analyses; 
Jour. Agr. Sci., Vol. IV, Part 2, p. 199, 1911. Also A Report of the 
Agriculture and Soils of Kent, Surrey, and Sussex; Board of Agriculture 
and Fisheries, 1911. See also: Loughridge, R. H., On the Distribution 
of Soil Ingredients among Sediments Obtained in Silt Analyses; Amer. 
Jour. Sci., Vol. VII, p. 17, 1874. Puchner, H., Tiber die Vertielung von 
'Ndhrstoffen in den Verschieden Feinen Bestandteilen des Boden; Landw. 
Ver. Stat., Band 66, Seite 463-470, 1907. Hendrick, J., and Ogg, W. J., 
Studies of Scoltish Drift Soil, Part I. The Composition of the Soil and 
of the Mineral Particles Which Compose It: Jour. Agr. Sci., Vol. VII, 
Part 4, pp. 458-469, Apr. 1916. McGeorge, W. T., Composition of Ha- 
waiian Soil Particles; Ilaw. Agr. Exp. Sta., U. S. Dept. Agr., Bui. 42, 
Jan., 1917. Robinson, G. W., Studies of the Palcpsoic Soils of North 
Wales; Jour. Agr. Res., Vol. VIII, Part 3, pp. 380-381, June, 1917. 

* McGeorge 's investigation of the residual volcanic soils of Hawaii 
Bhows some noteworthy exceptions to the work of Failyer and Hall in 



THE SOIL PARTICLE 



79 



Table XIV 

COMPOSITION OF SOIL SEPARATES (HALL) 



Separate 


SiO^ 


Al,03 


Fe,Oa 


CaO 


MgO 


K.O 


P=0. 


Coarse Sand (1 — .2 mm.) 


93.9 


1.6 


1.2 


.4 


.5 


.8 


.05 


Fine Sand (.2— .04 mm.) 


94.0 


2.0 


1.2 


.5 


.1 


1.5 


.1 


Silt (.04— .01 mm.) 


89.4 


5.1 


1.5 


.8 


.3 


2.3 


.1 


Fine Silt (.01— .002 mm.) 


74.2 


13.2 


5.1 


1.6 


.3 


4.2 


.2 


Clay (Below .002 mm.) 


53.2 


21.5 


13.2 


1.6 


1.0 


4.9 


.4 



43. Value of a mechanical analysis. — It is evident that a 
proper interpretation of a mechanical analysis will throw con- 
siderable light on the probable condition of a soil, especially 
physically. To the trained observer the preponderance of 
sand, clay, or silt signifies the probable presence of certain 
physical properties, which may affect the plant not only me- 
chanically but physiologically as well, through air, water, and 
nutrient movement. 

The chemical and mineralogical phases of such interpreta- 
tion are also worthy of consideration, as the proportion of the 
various separates determines whether the essential nutrient 
will be present in sufficient quantities to permit normal crop 
growth. Thus a mechanical analysis not only enlightens as 
to the general properties of a given soil, but when correlated 
with other factors is to some extent a criterion of agricultural 
value and crop adaptation. Some authors maintain that in 
the investigation of any soil a mechanical analysis should first 
be made, as it throws much light on many properties of a soil. 

44. Soil class — ^how soils are named. — As a soil is not 
composed of particles of uniform size and shape, a blanket 
term is needed, which will not only give some idea of the 
textural character of the mixture, for every soil is a mixture, 

that he found the lime and magnesia higher in the coarser particles and 
the silica higher in the finer separates. McGeorge, W. T., Composition 
of Hawaiian Soil Particles; Haw. Agr. Exp. Sta., Bui. 42, Jan. 1917. 



80 



NATURE AND PROPERTIES OF SOILS 



but at the same time will name it in such a manner as to reveal 
its general physical peculiarities and proportions. For this 
class names, such as sandy loam, loam, silt loam, and the 
like, are used. Class differs from texture, however, in that it 
has reference to the properties exhibited by a soil rather than 

Ci RAVEL SAHb LOAM CLAY 




^^ 



'f .K 



^^^ 



/ r^ 



v^ / ^' <^ 4 



<fy/ 






Fig. 16. — Diagram showing in a general way the mechanical compo- 
sition of gravel, sand, loam and clay soils and indicating in addi- 
tion how some of the more common field names arise. 



to any absolute grain size. Consequently, there may be a 
number of class names depending on the proportionate mix- 
tures of different sized particles that occur in the field. 

Class names have originated through long centuries of agri- 
cultural observations, but of late they have been more or less 
standardized because of the necessity of a definite nomen- 
clature. In general, the names used for the soil classes are the 



THE SOIL PARTICLE 



81 



same as those employed in mechanical analyses to designate 
the soil separates. This is rather unfortunate, but it obviates 
the increase of technical terms and a little care will prevent 
confusion in this regard. Four fundamental groups of soil 
are recognized: gravel, sand, loam, and clay (See Fig. 16). 
Gravel is a soil constituent that does not often occur alone 
and is not of great importance agriculturally because of its 
low fertility. The other three, however, either alone or in 
combination make up most of the arable soil. Their average 
mechanical analyses are set forth in Table XV. 

Table XV 

MECHANICAL ANALYSES OF SANDY, LOAMY AND CLAYEY SOILS^ 



Separates 


Sandy 
Soil 


Loamy 
Soil 


Clayey 
Soil 


1. Fine Gravel 

2. Coarse Sand 

3. Medium Sand 

4. Fine Sand 

5. Very Fine Sand. . . . 

6. Silt' 


% 

2 

15 

23 

37 

11 

7 

5 


% 

2 

5 

5 

15 

17 

40 

16 


% 
1 
3 
2 
8 
8 

36 


7. Clay 


42 



The sand group includes all soils of which the silt and clay 
separates make up less than 20 per cent of the material by 
weight. Its properties are, therefore, characteristically sandy 
in contrast to the more open character of gravel and the 
stickier and more clayey nature of the heavier groups of soil. 
A soil to be clay must carry at least 30 per cent, of the clay 
separate. It may even have more silt than clay but, since 
the silt particles impart clayey characters, as long as the per- 
centage of clay is 30 or above, the class name must remain 
clay. 

^ Whitney, M., The Use of Soils East of the Great Plains Eegion; 
U. S. Dept. Agr., Bur. Soils, Bui. 78, p. 12, 1911. 



82 NATURE AND PROPERTIES OF SOILS 

The loam class is rather difficult to explain. In mechan- 
ical composition it is more or less midway between sand and 
clay. A loam may be defined as such a mixture of sand, silt, 
and clay particles as to exhibit sandy and clayey properties 
in about equal proportions. It is a half and half mixture 
on the basis of properties, although the sum of the sands and 
the sum of the silt and clay are generally near 50 per cent., 
respectively. (See Fig. 16.) Because of the marked inter- 
mixture of coarse, medium, and fine particles, loams are 
usually soils of good physical character. They generally pos- 
sess the desirable qualities both of sand and clay without 
exhibiting those undesirable properties, such as extreme loose- 
ness and low water capacity on the one hand and stickiness, 
compactness, and slow air and water drainage on the other. 
Most of the better soils are some type of loam. 

It is obvious that in the field not only various kinds of 
gravelly, sandy, loamy, and clayey soils must occur, but the 
groups must grade into each other, thus giving rise to a con- 
siderable number of field names. (See Fig. 16.) These field 
names are listed below : 

Common Class Names 



1. 


Gravel 


9. 


Veiy fine sandy loam 


2. 


Coarse sand 


10. 


Loam 


3. 


Medium sand. 


11. 


Silt loam 


4. 


Fine sand 


12. 


Silty clay loam 


5. 


Very fine sana 


13. 


Clay loam 


6. 


Coarse sandy loam 


14. 


Clay 


7. 


Sandy loam 


15. 


Heavy clay 


8. 


Fine sandy loam 


16. 


Sandy clay 



The meaning of these names should be clear except possibly 
those into which the loam group is divided. Loam, as already 
explained, refers to a soil possessing in about equal amounts 
the properties imparted by the various separates. If, how- 
ever, we have practically the same condition but with one 



THE SOIL PARTICLE 



83 



size of particle predominating, tlie name of that particular 
separate is prefixed, giving still more data regarding the soil 
in question. Thus, a loam in which clay is dominant will be 
classified as a clay loam. In the same way, we may have a 
sandy loam, silt loan^ and so on. It is to be noted that the 
loams make up half of the class names. In fact, the greater 
proportion of the soils so far classified in the United States 
are loams, which is fortunate as the loams in general are more 
favorable for crop production than any of the other class 
groups. 

The mechanical analyses of some of the more common 
classes^ are listed in Table XVI : 

Table XVI 



Coarse Sands. . . . 

Sands 

Fine Sands 

Sandy Loams. . . . 
Fine Sandy Loams 

Loams 

Silt Loams 

Sandy Clays 

Clay Loams 

Silty Clay Loams 
Clays 



Fine 

Gravel 



12 

2 

1 

4 

1 
2 

1 
o 

1 


1 



Coarse 
Sand 



31 
15 
4 
13 
3 
5 
2 

8 
4 

2 
3 



Medium 
Sand 



19 

23 

10 

12 

4 

5 

1 

8 

4 

1 

2 



Fine 
Sand 



20 
37 
57 
25 
32 
15 

5 
30 
14 

4 



Vert 
Fine 
Sand 



6 

11 
17 
13 
24 
17 
11 
12 
13 

7 



Silt 



7 
7 
7 
21 
24 
40 
65 
13 
38 
61 
36 



Clay 



5 
5 
4 
12 
12 
16 
15 
27 
26 
25 
42 



It is evident that a mechanical analysis of a soil is nothing 
more or less than an expression of class, and the inferences 
that may be derived from either are in general the same. This 
leads to a consideration of class determination. 

45. Determination of soil classes.— The common method 
of class determination is that employed in the field. It con- 

^ Whitney, M., The Use of Soils East of the Great Plains Begion; 
U. S. Dept. Agr., Bur. Soils, Bui. 78, p. 12, 1911. 



84 NATURE AND PROPERTIES OF SOILS 

sists in an examination of the soil as to color, an estimation of 
its organic content, and, especially, a testing of the ' ' feel ' ' of 
the soil in order to decide as to the class name. Probably as 
much can be judged as to the texture and class of a soil merely 
by rubbing it between the thumb and the fingers or in the 
palm of the hand as by any other superficial means. This 
method is used in all field operations, especially in soil survey 
work. It really consists in sufficiently recognizing the textural 
composition of a soil that the class name may be determined.^ 

The accuracy of such a determination depends largely on 
experience. Inaccuracies are likely to occur in distinguishing 
between the various finer grades of soil ; for this reason, more 
nearly exact methods are necessary at times, especially in 
checking soil survey work or in carrying out investigations in 
which absolute accuracy is required. 

As a mechanical analysis of a soil is really a percentage 
expression of texture, it presents an exact method for class 
determination. For detailed work, somewhat complicated 
tables^ have been arranged; but the following diagram 

* Key for the practical classification of mineral soils : 

I. Soils possessing the properties of one size of 
particle largely. 

1. Particles very large Gravel 

2. Particles apparent to eye; feel gritty and 
non-plastic Sands 

3. Particles very small ; soil very plastic when 

wet, hard when dry Clay or 

Sandy Clay 

II. Soils possessing the properties of a number of 
sizes of particles — a mixture. 

1. A fairly equal exhibit of sandy and 
clayey properties Loam 

2. A mixture but with sand predominating. . .Sandy Locum 

3. A mixture but with silty character dom- 
inant. The soil has a floury or talc feel 

and is quite plastic when wet Silt Loam 

4. A mixture but with clayey characters very 
apparent. Soil is very plastic and ap- 
proaches a clay in character Clay Loam 

^Bur. of Soils, Soils Survey Field Boole, p. 17; U. S. Dept. Agr., Bur. 
Soils, 1906. Also, Bur. Soils, Bui. 78, p. 12, 1911. 



THE SOIL PARTICLE 



85 



(Fig. 17), devised by Whitney/ presents a simple method for 
the identification of a soil from a mechanical analysis. The 
convenience of such a triangular representation is obvious. 

CLAY 
100 




10 20 50 40 50 60 70 80 90 100 

PER CENT 



SILT 



Fig, 



17. — Diagram for the determination of class from a mechanical 
analysis. In using the diagram the points corresponding to the 
percentages of silt and clay are located on the silt line (abscissa) 
and clay line (ordinate) respectively. Perpendiculars at these 
points are then projected inward until they intersect. The name 
of the compartment in which the intersection occurs gives the class 
name of the soil in question. 



46. Soil survey classification — soil type. — The function 
of the soil survey is to investigate the nature and occurrence 

^Whitney, M., The Use of Soils East of the Great Plains Region; 
U. S. Dept. Agr., Bur. Soils, Bui. 78, p. 13, 1911. 



86 NATURE AND PROPERTIES OF SOILS 

of soils in the field. The soils thus studied are classified into 
areas having approximately the same crop relations and tillage 
properties. The location of the areas of each kind of soil is 
represented on an adequate base map, and their character and 
chief economic and agricultural relations are described in a 
printed report accompanying the soil map.^ (See Fig. 18). 

In classifying soils six primary factors are considered. 
These, beginning with the broadest, are as follows: (1) tem- 
perature, (2) precipitation, (3) agency of formation, (4) kind 
of material, (5) special properties other than texture, and 
(6) texture. It is obvious that certain soils may be of different 
texture but alike in all other ways. Their climatic environ- 
ments, mode of formation, rock materials, and specific prop- 
erties, such as color, drainage, organic condition, and lime 
content may be approximately the same. Such soils are 
grouped together as series and the series are named, generally 
from some town, county, or river of the near vicinity. Thus 
we have the Norfolk series of the Atlantic coastal plain; the 
Cecil soils of the Piedmont Plateau ; the Ontario series arising 
from the calcareous till of central New York state and the 
Marshall soils of the loessial region of the Middle West. The 
soils within each series are approximately the same except for 
class distinction. 

The soil type is the unit of classification and may be defined 
as an area of soil alike in all characteristics, including crop 
productiveness. Obviously any soil class of any particular 
series would be a soil type. Norfolk sandy loam, Ontario loam, 
and Cecil clay are examples of how soil types are designated. 
The type designation is especially valuable in soil description 
since the series name expresses in one word a great number of 
conditions, which otherwise would require detailed explana- 
tion. The class name establishes in addition the textural con- 
dition. 

^ For further information consult one of the numerous soil survey 
reports as published by the U. S. Dept. Agr., Bur. of Soils. 



Bui. 60, Bureau of Soils, U. S. Dept. of Agriculture 




Volusia 
silt loam 



V'o/itsla Dunkirk Il,(ntin<jto/i Dunkirk Muck 

loam gravelly loam loam ^.j^y 



Fig. 18. — Part of the Madison County, New York, soil map showing the 
topography and drainage ami the relation of the various soil types 
to one another. The Volusia series arises from the ground moraine, 
the Dunkirk from glacial lake sediments while the Huntington is 
alluvial. Note the varying elevation of the muck. 



THE SOIL PARTICLE 87 

While the principles of series identification are too com- 
plicated to be expanded farther at this time, enough has been 
said to establish the importance of accurate soil classification. 
Unless soils are accurately named in soil survey work, the map 
and its accompanying report are useless. 

Soil texture and class are thus the basis for practical soil 
study, whether regarding some particular property or a gen- 
eral condition, such as crop adaptation. No matter what the 
phase of soil study may be, texture and class are sure to have 
some important influence and must be considered in the in- 
vestigation. 

47. Soil structure. — While texture is of great importance 
in determining tlie general characteristics of a soil, it is evi- 
dent that the arrangement as well as the size of the particles 
must exert some influence. The term structure is used to refer 
to this arrangement or grouping. It is at once apparent that 
soil conditions — such, for example, as air and water move- 
ment, heat transference, and the like — will be as much affected 
by structure as by texture. As a matter of fact, the great 
changes wrought by the farmer in making his soil better 
suited as a foothold for plants are structural rather than 
changes in texture. The compacting of a light soil or the 
loosening of a heavy one is merely a change in the arrange- 
ment of the soil grains and in the condition and nature of the 
colloidal complexes^ thereof. 

From the standpoint of size and arrangement of particles 
there are really two classes of soils, those of single grain struc- 
ture and those which are complex, the particles both large 
and small being bound together by indefinite colloidal com- 
plexes. The former condition is of course best exemplified 
by a sand. Such a soil is loose and open with large individual 
pore spaces and ready circulation of air and water. The com- 

* Material in a colloidal state has a great deal to do with all soil 
phenomena. Its characteristics and influence must be kept constantly in 
mind in soil study. 



88 NATURE AND PROPERTIES OF SOILS 

plex structure is best developed in clay. Here the soil gran- 
ules are made up of many particles, the colloidal material act- 
ing as a binding agent. Such a soil may be loose, open and 
friable, if granules of the proper size and nature are developed. 
On the other hand, improper handling may run the complexes 
together and an impervious and puddled condition may result. 
The sand will obviously permit of no very great structural 
change, while the clay can be modified very materially by 
certain field manipulations. 

The ideal structural condition is most likely to occur in a 
loam soil. In such a soil some of the particles are large and 
function separately ; others are medium in size and tend to 
form the nuclei around which smaller particles, both colloidal 
and non-colloidal, may cluster to form granules, or aggregates. 
There are thus a few large pore spaces which facilitate drain- 
age, and numberless small openings in which water is retained. 
Air, therefore, finds easy movement and sanitation is pro- 
moted. In promoting such a condition the organic matter 
plays an important part. It usually exists as a dark, partially 
decayed material, often colloidal in nature. It pushes apart 
the grains and lightens the soil, and contributes much in bring- 
ing about the loamy condition so favorable to plant develop- 
ment. It is a valuable addition also on account of its water- 
holding capacity and its nitrogen content. 

48. Specific gravity of soils. — The texture, as well as the 
structure of a soil, has considerable influence on certain phys- 
ical conditions other than those already mentioned. One of 
these is weight. The weight of a soil is determined by two 
factors : the weight of the individual particles and the amount 
of the space occupied by the soil material. The former is 
determined by the chemical and mineralogical character of 
the particles, the latter by their structural arrangement. Thus, 
if the soil particles are heavy and the soil is compact, the 
weight of any given volume, a cubic foot for example, will be 
high. 



THE SOIL PARTICLE 



89 



The specific gravity^ of a soil is obviously the average spe- 
cific gravity of the particles. It is unaffected by the structure, 
remaining the same whether the soil is loose and open or com- 
pact and unaerated. Although a great range is observed in 
the specific gravities of the common soil minerals^, the spe- 
cific gravity of a purely mineral soil varies betveeen the nar- 
row limits of 2.6 and 2.7. This occurs because quartz and 
feldspar, whose specific gravities are about 2.65 and 2.57, 
respectively, usually make up the bulk of the mineral portion 
of most soils. The fineness of the particles seems to have no 
appreciable effect on specific gravity as shown by the follow- 
ing data from Whitney and Smith^ : 

Table XVII 

SPECIFIC GRAVITY OF SOIL SEPARATES 



Separates 



Fine gravel. . . 
Coarse sand. . . 
Medium sand. 
Fine sand .... 
Very fine sand . 

Silt'. 

Clay 




Smith 



67 
64 
64 
69 
66 
65 
66 



^ Specific gravity is expressed as a ratio of the weight of any volume 
of a substance to the weight of an equal volume of some other substance 
taken as a standard unit. Liquids and solids are usually compared with 
water at its maximum density (4° C). 

^ The specific gravities of some of the common soil minerals are as 
follows: 



Quartz 2.60 2.70 

Orthoclase 2.57 

Plogioclase 2.62-2.76 

Muscovite 2.76-3.00 

Biotite 2.70-3.10 

Hornblende 3.05-3.47 

Augite 3.20-3.60 



Apatite 3.20 

Kaolinite 2.60-2.63 

Serpentine 2.50-2.65 

Chlorite 2.65-2.92 

Epidote 3.25-3.50 

Hematite 4.90-5,30 

Limonite 3.60-4.00 



'Whitney, M., Sovie PhfisicaJ Proiieriies of Soils; U. S. Dept. Agr., 
Weather Bur., Bui. 4, 1892. Smith, Alfred, Belation of the Mechanical 
Analysis to the Moisture Equivalent of Soils; Soil Sci., Vol. IV, No. 6, 
p. 472, Dec, 1917. 



90 NATURE AND PROPERTIES OP SOILS 

The only marked variation here observed is in the clay 
separates of the first column. This may be due to the concen- 
tration of the iron-bearing silicates in this grade and would 
thus be an apparent rather than a real variation. 

Only one condition may vary the specific gravity of any 
soil. This is the quantity of organic matter present. As the 
specific gravity of organic matter usually ranges from 1.2 to 
1.7, the more that is present the lower will be the figure for 
any given soil. A purely organic soil, such 
as muck, presents a variable specific grav- 
ity ranging from 1.5 to 2.0, according to 
the amount of inorganic wash it has re- 
ceived from external sources. Some highly 
organic mineral soils may drop as low as 
50 \ 2.3. Nevertheless, for general calculations, 
GRAMM the average arable soil may be considered 

to have a specific gravity of about 2.65. 
The specific gravity of a soil is generally 
Fig. 19. — Drawing determined by means of a picnometer, a 
f picnom^r hottle fitted with a perforated ground-glass 
generally used in stopper and accurately calibrated (Fig. 
specifiTgravity of 1^). By comparing the weight of the total 
soil. The ground- water held by the bottle, usually 50 cubic 
perforatedT^^ ^^ centimeters, with the weight of the water 
when any given amount of dry soil, say 5 
grams, is present in the bottle, the weight of the water dis- 
placed by the soil can be determined and the specific gravity 
calculated therefrom.^ 

* Below will be found a sample calculation : 

Weight of picnometer 23.257 grs. 

Volume of picnometer 50 cc. 

Wt. of picnometer + 5 grs. soil + X grs. water. . . .76.347 grs. 

Wt. of picnometer + 5 grs. soil 28.257 grs. 

Wt. of X grs. water 48.090 gi-s. 

Water displaced (50 — 48.09) 1.910 gra. 

Specific gravity ^ " = 2.61 + 




THE SOIL PARTICLE 91 

49. Volume weight of soils. — The actual weight of dry 
soil in any g-iven volume is generally expressed by volume 
weight, a figure indicating the number of times heavier the 
dry soil is than the water that will occupy the same soil vol- 
ume. Thus, if the dry soil in a cubic foot of space weighs 
99.8 pounds, the volume weight would be 99.8^62.42 or 1.6. 
The volume weight differs from specific gravity in that it 
compares the weight of the dry soil to the weight of water 
that will occupy the total soil volume — that is, the space 
usually filled by soil i^articles, soil air, and soil water. Specific 
gravity, however, compares the weight of the dry soil to that 
of water that will occupy only the volume of the particles 
alone, taking no consideration of the normal pore space. It 
is consequently always the higher figure.^ 

This volume weight figure depends on the texture of the 
soil, the structure and the amount and condition of the organic 
matter. The particles of sandy soils always tend to lie in 
close contact, thus increasing the weight of soil to a given 
volume. The particles of the finer soils, such as silt loams, 
clay loams, and clays, on the other hand, being smaller and 
lighter, do not lie so closely together, A greater total pore 
space is, therefore, usually present in the finer soils and the 
volume weight is correspondingly lov^^ered. Mineral soils may 
range in volume weight from 1.10 to 1.35 for clay to 1.55 to 
1 . 70 for sand.- The influence of texture on the volume weight 
is thus evident. 

The structural and organic condition of soils often pro- 
duces wide variation in volume weight. When a soil is loos- 

* As a soil is compacted, its volume weight increases due to the increase 
volume occupied by the soil particles and the corresponding decrease in 
pore space. If it were possible to compact a soil to a completely solid 
condition, its volume weight would approach its specific gravity as a 
limit. Specific gravity represents, therefore, 100 per cent, soil particles. 
Volume weight in comparison indicates the proportion of space occupied 
by the soil particles. 

^ Sandy soils are commonly spoken of as light soils, while clays are 
called heavy. Such usage refers to working properties and has no 
reference to actual weights. 



92 NATURE AND PROPERTIES OF SOILS 

ened through tillage, it becomes lighter for any given volume. 
The addition of organic matter has the same effect, since the 
particles are spread wider apart and the air and water spaces 
increased. The specific gravity figure of a sandy loam of 1.55 
may readily be lowered to 1.45 by an increase of organic 
material. Some loams high in organic matter may drop as 
low as 1.1 in specific gravity while muck often reaches the 
low figure of .40. 

In the field the volume weight of a soil may be estimated by 
driving a cylinder of known volume into the ground and ob- 
taining thereby a core of natural soil. By weighing the soil 
and then determining the amount of water that it holds, the 
amount of absolutely dry soil may be ascertained. Dividing 
this by the weight of an equal volume of water gives the figure 
for volume weight.^ 

A laboratory determination may be made by putting the 
soil into a receptacle of known volume and weighing it. From 
the weight of the absolutely dry soil and the weight of an 

* The rubber tube method has proven very convenient for the field de- 
termination of volume weight. A hole is bored in the soil to the required 
depth by a specially constructed auger, the soil being carefully removed 
and later oven dried. A very thin-walled tubular rubber bag of the size 
of the auger hole is carefully inserted in the hole previously bored. The 
tubular bag is then filled with water flush with tlie surface of the soil. 
The water is measured and the volume of the soil removed is thus de- 
termined. Knowing the weight of dry soil and its original volume, the 
volume weight may be calculated. The experimental error of the method 
is rather low. 

Israelsen, O. W., A Neiv Method of Determining Volume Weight; 
Jour. Agr. Ees., Vol. XIII, No. 1, pp. 28-35, April, 1918. 

The paraffin-immersion is valuable with heavy soils. Small pieces of 
soil are dried, weighed and then coated very thinly with paraffin, just 
sufficiently to prevent the entrance of water, yet not enough to intro- 
duce serious experimental error. The weight of the water displaced by 
a number of such pieces may be determined easily by the use of a 
graduated cylinder. 

Shaw, C. F., A Method for Determining the Volume Weight of Soil 
in Field Condition; Jour. Amer. Soc. Agron., Vol. IX, No. 1, pp. 38-42, 
1917. See also, Trnka, E., Sine Studie iiber einige physikalishchen 
Eigenschaften- des Bodens; Internat. Mitt, of Bodenkunde, Bd. IV, Heft 
4-5, S. 363-380, 1914. 



THE SOIL PARTICLE 93 

equal volume of water, the volume weight may be calculated. 
This method will give only approximate results, however, as 
the structural relationships are more or less artificial.^ 

50. Actual weight of soil. — When the volume weight of 
a soil is known, its weiglit in pounds to the cubic foot may be 
found by multiplying by 62.42. Soils may vary in weight 
from 68 to 80 pounds for clays and silts to 100 to 110 pounds 
for sands. The greater the organic content, the less is this 
weight to the cubic foot. A muck soil often weighs as little 
as 25 or 30 pounds. This weight, of course, is for absolutely 
dry soil and does not include the water present, which may be 
much or little, according to circumstances. 

The actual weight of soil may also be expressed in acre-feet. 
An acre-foot of soil refers to a volume of soil one acre in 
extent and one foot deep. In the same way we may have 
an acre-eight-inches or an acre-six-inches. The weight of an 
acre-foot of soil usually varies from 3,500,000 to 4,000,000 
pounds. The standard usually adopted is 2,000,000 pounds, 
being the weight of average soil to a depth of 6-/3 inches. 
The value of knowing the actual weight of a soil lies in the 
possibility of calculating thereby the amount of water, the 
amount of organic matter, or the actual number of pounds of 
the mineral constituents present in the soil. Such informa- 
tion affords another means of comparing two soils. 

51. Pore space of soil. — The pore space of soil is occu- 
pied by air and water in constantly varying proportions. The 
amount of this pore space is determined by the texture and 
the structure of the soil. As already emphasized, the coarser 

^ A comparison of the four methods is given by Israelsen, O. W., A 
NeuJ MctJiod for Bctermininq Volume Weight; Jour. Agr. Ees., Vol. 
XIII, No. 1, p. 32, 1918. 

Average Volume Weight of Tehama Clay to a Depth of 60 Inches. 

Laboratory method on disturbed soil 1..35 ± .008 

Kubber tube method 1.74 ± .010 

Iron cylinder method 1.73 

Paraffin-immersion method 1.73 ± .035 



94 NATURE AND PROPERTIES OF SOILS 

soils are heavy due to the close contact of the particles, while 
the finer soils are much lighter due to the tendency of the 
small particles to resist compaction.^ This means that soils 
such as sands and sandy loams contain less pore space than 
silt loams, clay loams, and clays. While the heavier soils have 
more combined air and water space, the individual spaces are 
much smaller than in the sands, which accounts for the slow 
air and water drainage in the former and the ease with which 
such phenomena take place in the lighter soils. 

A very simple formula may be used to calculate pore space, 
providing the specific gravity and volume weight are known. 
It is subject to considerable inaccuracy, however, because 
of the presence of colloidal matter, the exact influence of which 
cannot be determined. 

^ T^ ci -inn /vol. wt. 100 \* 
% Pore Space = 100 — 1 x ^j- 1 

A soil having a volume weight of 1 . 6 and a specific gravity 
of 2.6 has, according to this formula, 38,5 per cent, of pore 
space. A soil in which the above figures are 1,1 and 2.5, 
respectively, possesses 56 per cent, of air and water space. 

The following figures taken from King ^ illustrate the rela- 
tion that texture and, to a certain extent, structure also occu- 
pies in relation to soil pore space : 

^ Sandy soils are generally spoken of as loose, while clays are called 
compact. The term compact is thus used in the sense of hard, unyielding, 
stiff, or impenetrable, and does not indicate that the pore space of clay 
is less than that of a sandy soil. 

*It has already been explained in a previous footnote (see under 
volume weight) that the specific gravity of a soil represents 100 per 
cent, soil material or the weight of absolutely solid soil. Volume weight 
indicates in comparison thereto, the soil material actually present. The 
ration of the specific gravity to the volume weight when multiplied by 
100 becomes the percentage of the soil volume occupied by the soil 
particles. 

^ King, F. H., PJvysics of Agriculture ; published by the author, Madi- 
son, Wisconsin, 1910. 



THE SOIL PARTICLE 95 

Table XVIII 

PERCENTAGE PORE SPACE IN SOILS OF DIFFERENT TEXTURE 

Sandy soil 32.5 

Loam 34 . 5 

Heavy loam 44 . 1 

Loamy clay 45 . 3 

Clayey loam 47 . 1 

Clay 48.0 

Heavy clay 52 , 9 

The pore space in a normal soil is occupied by water and 
air. If the water content is low, the air space is large, and 
vice versa. Thus the relationships of the total pore space 
and the size of the individual spaces to the amount of air and 
water contained, to their movement through the soil, to soil 
sanitation, to root extension, to bacterial action, and to crop- 
ping conditions in general, become apparent. It is the regu- 
lation of this pore space that is really important in any struc- 
tural consideration. The effect on plant growth of a change 
of pore space is the only test of its advisability. 

52. Soil particles — ^their number and surface exposed. 
— Since soil particles run to extremely small diameters, the 
number in any given volume is very large, especially when 
fine-textured soils are considered. However, any calculation 
of the number of particles present in a soil is open to great 
inaccuracy j first, because it is impossible to get a correct fig- 
ure for the average diameter of the particles of any soil or of 
the various groups of separates that go to make it up ; and, 
secondly, because it must be assumed in the calculation that 
the particles are spherical. The presence of colloidal matter, 
especially in the heavier soil types, introduces an error the 
magnitude of which must be very great. Nevertheless, such 
a calculation, even if very inaccurate, gives some idea as to 
the immense number of grains that are present even in the 



96 NATURE AND PROPERTIES OF SOILS 

coarser soils. A few figures are given in Table XIX for some 
of the average soil classes ^ established by the Bureau of Soils : 

Table XIX 

APPROXIMATE NUMBER OF PARTICLES TO A GRAM OF VARIOUS SOIL 

CLASSES ^ 



Soil Class 



Number of Particles 
TO THE Gram 



Sands 

Sandy loams. 

Loams 

Clay loams. . 
Clays 



2,287,000,000 

5,483,000,000 

7,332,000,000 

11,877,000,000 

19,177,000,000 



An important property of the surface of the grains is the 
tendency toward the retention of soluble material in a par- 
tially or wholly available condition for plant use. This power, 
designated as absorption, is exhibited to a high degree by 
fine soils, in which the individual pore spaces are small and 
the amount of surface exposed is large, due to the presence 
of considerable colloidal matter. This capacity is an especially 
important factor in the economical use of fertilizer salts. Ab- 
sorption may also, by bringing materials into closer contact, 
hasten or retard certain chemical actions. Changes may thus 

^ The mechanical analyses of these particular classes are given on 
page 83. 

^ The number of particles in any soil sample may be arrived at from 
a mechanical analysis and the diameters that limit each group. Using 
the average diameter of each group together with the percentage of 
the groups in a given sample, the number of particles may be calculated 
by the following formula: 

,-r , „ ^. , . 1 J. -1 Weight of sample in grams 

Number of particles in a sample of soil = " ,^ — =-t^ — tt-ph^ 

1/6 jt D' X 2.65 

The formula 1/6 jj C is that used for determining the volume of a 
sphere^ the diameter in this case being expressed in centimeters. When 
multiplied by the average specific gravity of soil particles the weight of 
an average particle is obtained in grams. In the above calculations, 
2.7 was used instead of 2.65. 



THE SOIL PARTICLE 



97 



be expected to go on in the soil that would not take place in 
the laboratory beaker. The relation of this absorption to bac- 
terial activity also cannot be overlooked. 

The minerals of the soil are all very resistant to solution; 
if they were not, they would long ago have been leached away. 
Such materials, while almost insoluble under ordinary cir- 
cumstances, allow appreciable amounts of nutrients to appear 
in the soil solution, because of the immense amount of surface 
exposed, although the specific solubility remains the same. 

In order to present some idea of the internal surface of 
ordinary soils, a few figures are given on the same soil classes 
for which the number of particles have already been calcu- 
lated : 

Table XX 

APPROXIMATE INTERNAL AREA OF SEVERAL AVERAGE SOIL 
CLASSES ^ 



Soil Class 


Square 

Inches 

per Gram 


Square 

Feet per 

Pound 


Acres per 
Acre-Foot of 
3,500,000 LBS. 


Sands 


89 
213 
294 
430 
653 


280 

671 

926 

1354 

2057 


22,549 


Sandy loams 

Loams 

Clays loams 

Clays 


53,965 

74,410 

108,830 

165,270 



While these figures are as grossly inaccurate as those re- 
garding the number of particles, they tend to emphasize the 
tremendous internal surface possessed by even the coarser 
soils. The data presented for an acre-foot of soil, while al- 
most too large for adequate comprehension, are probably 
much too low. It is not to be wondered at that the slowly 
soluble minerals are able to supply sufficient nutrients to the 

^ When the approximate number of particles and their sizes in any 
given weight of soil are known, the internal surface may be calculated 
by the following formula: 

Surface = jj D^ X number of particles. 



98 NATURE AND PROPERTIES OP SOILS 

crop growing on the soil, when such a large amount of sur- 
face is continually available for chemical action. 

53. Resume. — The discussion of the soil particle as to its 
size, its classification, its chemical characteristics, and its 
mineralogical peculiarities is undoubtedly important. Im- 
portant also are the specific physical properties which arise 
because of textural and structural make-up, such as specific 
gravity, volume weight, pore space, and immense internal 
surface. These phases, however interesting in themselves, 
must not be studied so closely as to prevent their broad and 
vital plant correlations from becoming evident. None of the 
transformations concomitant with normal crop production 
takes place in the soil without definite and widespread co- 
operation. The study of the soil particle is, therefore, more 
than a consideration of a few interesting physical and chem- 
ical phenomena. From such investigations have been devel- 
oped and perfected the broad principles which govern suc- 
cessful soil management and economical food production. 



CHAPTER V 
THE ORGANIC MATTER OF THE SOIL 

One op the essential differences between a soil and a mass 
of rock fragments lies in the organic content of the former. 
Organic matter is necessary in order that mineral material 
may become a soil and that it may grow crops successfully. 
The physical condition of soils depends largely on the pres- 
ence of organic matter and chemical reaction is greatly ac- 
celerated by its decay. 

In the process of soil formation the addition of organic 
materials is more or less a secondary step. In residual debris 
the amount of organic matter held by the growing soil in- 
creases as the process of weathering goes on; in glacial soils, 
however, the matrix or skeleton of the soil is already formed 
before there is an opportunity for organic matter to become 
incorporated in it. The final result from the mixing of min- 
erals and their weathered and altered products with the 
decayed or partially decayed organic matter that is sure to 
accumulate, is a mass much more complicated than either 
of the original constituents. The complexity of the average 
soil has already been sufficiently stressed. 

54. The source of soil organic matter^ and the char- 
acter of plant tissue. — The source of practically all soil 

^ The soil organic matter includes not only all compounds contained 
in the original vegetable and animal tissues but also those existing in 
the partially decayed portions of such material. Carbon dioxide, methane 
and like compounds are usually not considered as a part of the soil 
organic matter. In this respect, the above definition is narrower than 
that for organic chemistry, which is the chemistry of carbon compounds. 
For a very good review of literature on soil organic matter, see Morrow, 
C. A., The Organic Matter of the Soil: A Study of the Nitrogen Distri- 
iution in Different Soil Types; Dissertation, Univ. Minn., 1918. 

99 



100 NATURE AND PROPERTIES OF SOILS 

organic matter is plant issue.^ Some of this matter ac- 
cumulates from the above-ground parts of plants that have 
died and fallen down to become mixed with the surface soil; 
the remainder is a result of root extension and subsequent 
decay. The organic matter of the surface soil is derived from 
the tops and the roots of plants growing on it, while that of 
the subsoil is very largely a result of root extension and sub- 
sequent decomposition. 

Since soil organic matter has its origin very largely from 
the higher plants, it is advisable to consider the general chem- 
ical nature of such material.- About 75 per cent, of average 
green plant tissue is water. The dry matter is made up of 
carbon, oxygen, hydrogen, and mineral material in the ap- 
proximate ratio of 6, 5, 1 and 1 respectively. The preponder- 
ant elements of normal plant tissue are evidently carbon, 
oxygen, and hydrogen. (See Fig. 20.) 

It is usual in classifying the compounds in plants to group 
them under the following heads: (1) carbohydrates, (2) 
fixed oils and waxes, (3) volatile oils and resins, (4) organic 
acids and their salts, and (5) nitrogenous compounds.^ The 

^ It must not be inferred that higher plants are the only source of soil 
organic matter. Assuming that the weight of one bacterial cell is 
.000,000,002 of a milligram and that in each gram of a normal fertile 
soil, weighing 2,000,000 pounds to an acre-seven inches, there are 
100,000,000 of such organisms, the weight of bacteria alone would be 
400 pounds to the surface acre. This is a very conservative estimate, 
800 pounds probably being more nearly correct. Considering the molds, 
fungi, algae, actinomycetes, insects, and earthworms, there are probably 
2000 pounds of living material in every acre of normal soil exclusive 
of plant roots. These organisms in their functioning supply no insig- 
nificant portion of the soil organic matter. 

^ For a fuller discussion see : Ingle, Herbert, Manual of Agricultural 
Chemistry, Chap. X, London, 1913. Also, Stoddard, C. W., The Chem- 
istry of Agriculture, Chap. Ill, Philadelphia and New York, 1915, 
Also, Thatcher, E. W., The Chemistry of Plant Life, New York, 1921. 

' I. Carbohydrates — Sugars, starch, cellulose, legnin, inulin, gums, 
pectins, and pentosans. 

II. Fixed oils and waxes — Castor oil, corn oil, cottonseed oil, linseed 
oil, and the like. 

III. Volatile oils and resins — Oil of mustard^ of cloves, of pepper- 
mint, etc. Eosin, myrrh, balsam, etc. 



THE ORGANIC MATTER OF THE SOIL 101 

mineral matter or so-called ash exists as a part of the com- 
pounds listed under these headings. The carbohydrates, hav- 
ing the general formula of C^i'H.^O)^ include such compounds 
as starch, cellulose, dextrose, glucose, cane sugar, and the like. 
The fats and oils may be represented in plants by such glycer- 
ides as butyrin, stearin, olein, palmitin, while many acids of 
an organic nature exist especially in fruits and vegetables. 




Fig. 20, — Diagram showing the general composition of green plant tissue. 
The nitrogen which is generally less than .5 per cent, is included 
with the ash in the above diagram. (After Stoddard.) 

Of the five groups, however, the nitrogenous compounds are 
probably the most complicated as they carry not only carbon, 
hydrogen, oxygen, and nitrogen, but also mineral elements 
such as sulfur, phosphorus, calcium and iron. They are com- 
pounds of high molecular weight and many are of unknown 

IV. Organic acids and their salts — Citric acid, malic acid, tannic acid, 
tartaric acid, and the like. 

V. Nitrogenous compounds — Nitrates, ammonia, amides, amino-aeida, 
alkaloids, and proteins. 



102 



NATURE AND PROPERTIES OF SOILS 



constitution. Simple proteins, such as albumin, globulin, pro- 
tamins, and others, are found in plants, besides certain de- 
rived proteins such as proteosis and peptones. In addition 
to all these, there is a host of other nitrogenous compounds 
that have no small influence on the composition of the soil 
organic matter.^ 

It is also necessary to consider that certain portions of the 
cell contents and cell walls are in a collodial state. Such a 
condition is important as the translocation of dissolved sub- 
stances from soil to plant and iTom cell to cell depend largely 
on their diffusibility through colloidal membranes. 

It is evident even from this brief discussion that the chem- 
ical character of plant tissue is far from simple. The degra- 
dation of such material, especially in the presence of com- 
plex mineral products, generally gives rise at first to com- 
pounds no simpler; in fact, the chances are that the result- 
ing compounds will be much more complicated. It is only 
later in the processes of decomposition that simple products 
result. 



^ Crops are usually analyzed for six constituents — water, ash, crude 
protein, crude fiber, nitrogen free extract, and crude fat. Water is 
determined by drying the sample at the temperature of boiling water. 
By burning a sample of the plant tissue until all of the organic matter 
has been driven off, the percentage of mineral matter may be found. 
Crude protein is obtained by mulptiplying the figure for total nitrogen 
by 6.25. Crude fat is found by extracting the dry plant tissue with 
ether, while the crude fiber is that which remains of the fat-free material 
after treatment with both dilute sulfuric acid and dilute sodium hydrox- 
ide solutions. Nitrogen-free extract is the difference between the sum 
of the above constituents and 100 per cent. Below are four typical 
analyses : 



Crop 


Water 

% 


Ash 

% 


Crude 
Protein 

% 


Crude 
Fiber 

% 


Nitrogen 

Free 
Extract 

% 


Crude 

Fat 

% 


Alfalfa (green) . . . 
Lettuce (fresh) . . . 
Wheat (grain) . . . . 
Timothy (hay) . . . . 


71.8 
94.7 
10.5 
13.2 


2.7 

.9 

1.8 

4.4 


4.8 

1.2 

11.9 

5.9 


7.4 

.7 

1.8 

29.0 


12.3 

2.2 

71.9 

45.0 


1.0 

.3 

2.1 

2.5 



THE ORGANIC MATTER OF THE SOIL 103 

55. Decomposition^ of organic matter in soils. — AVhile 
the general trend of organic degradation in soils is towards 
simplification, the process is by no means a progressive one. 
Many products are built up that are much more complex 
than the original tissue. Most of the fermentation and putre- 
faction is due to that great group of organisms called bacteria, 
although molds, fungi, and the like also are important. The 
action of these organisms may be direct, but is more likely 
to be enzymie." A cycle is therefore set up, in which the 
higher plants and animals are occupied in building up, while 
bacteria are tearing down and reducing the residue of plant 
action to simple forms, such as can be ultimately utilized again 
in plant nutrition. The importance of soil organisms is thus 
evident, and the encouragement of their growth and function 
is clearly a part of good soil management. (See Fig. 21.) 

When the complex molecules that make up plant tissue 
break down, they split along definite lines of cleavage, de- 
pending on the structure of the original molecule. These 
bodies, which are usually simpler in nature than those from 
which they have sprung, are called cleavage products, and 
without a doubt their appearance is the first step in organic 
decomposition. These compounds are subject to still further 
change, and because of the gi'eat number of agencies at work 
the secondary products that result may be simpler or more 
complex, according to conditions. Some bacteria have a tend- 
ency, while tearing down organic matter, to produce syn- 
thetic compounds, which present a very complicated molecule 
until they are in turn degraded. The tendency for the sec- 
ondary products to react both among themselves and with the 

^ Decomposition and decay are general terms referring to all of the 
degradation processes through which the original tissue passes in the 
soil. Fermentation refers to the decomposition of carbohydrates while 
putrefaction has to do usually with nitrogenous materials. 

^ A catalytic agent is a material capable of hastening or retarding a 
chemical reaction, the catalyst emerging unchanged from the transforma- 
tion. Enzymes are catalysts produced by living organisms and may be 
active within or without the cell. They are generally colloidal in nature. 



104 



NATURE AND PROPERTIES OF SOILS 



mineral constituents is by no means an unimportant factor 
in accounting for the complexity of the decaying organic mat- 
ter. 

As the processes of fermentation and putrefaction go on 
the complex intermediate compounds are gradually broken 
down and certain simple products result. Such materials may 
result from a progressive simplification of the partially de- 
li IGHER 
PLANTS 



NUTRIENTS 




PLANT 
TISSUE 



LOST FROM 
THE 
SOIL 



Fig. 21. — Diagram showing the transformations through which the con- 
stituents of the plant tissue pass from the time the organic matter 
enters the soil until it is in a condition to be used by succeeding 
crops. The cycle is very largely biological. 

cayed matter or may be by-products or split-off compounds 
from the more complex reactions. These simple materials are 
partially solid and partially gaseous. Carbon dioxide is a 
universal product of bacterial activity of all kinds and is 
constantly being evolved. Other simple constituents arising 
from organic decay are water, ammonia, nitrites, nitrates, free 
nitrogen, and sulfur dioxide. Some of these are lost from 
the soil, some lose their identity by reacting with the soil con- 
stituents, while others may function as plant nutrients. When 



THE ORGANIC MATTER OF THE SOIL 105 

they are absorbed again by a crop, the organic cycle is com- 
pleted. 

56. The partially decomposed organic matter.^ — The 
most complicated parts of the organic matter in the soil are 
the primary and secondary products of decomposition, the 
materials between the original tissue and the simple products. 
These compounds are not only complex but they are contin- 
ually changing. A certain compound present in the soil one 
week may be altered the next. Again, at least a part of the 
decomposing organic matter is colloidal, thus possessing spe- 
cial absorptive and catalytic properties. When the soil 
organic matter is treated with the various extractive agents, 
reactions may be induced which would not take place in a 
normal soil. Compounds are then formed which would prob- 
ably not exist under natural conditions. 

Many chemists have worked on the problems of the con- 
stitution of the organic matter of the soil and have published 
their results. The early conceptions were rather simple. 
Mulder,^ for example, considered the soil organic matter to 
consist almost entirely of carbon, hydrogen, and oxygen. Such 
a concept ignores the presence of nitrogen, sulfur, and the 
mineral elements of the original plant tissue, and is much 
too simple to explain organic transformations. 

Even the investigators ^ of Mulder 's time obtained discor- 

^ See Morrow, C. A., The Organic Matter of the Soil ; A Study of the 
Nitrogen Distribution in Different Soil Types; Dissertation, Univ. 
Minn., 1918. 

^Mulder, T. J., Die Organischen Bestandtheile im Boden ; Chemie der 
Ackerkrume, I, pp. 308-360, Berlin, 1863. Also, Wiley, H. W., Agricul- 
tural Analysis; Vol. I, p. 53, Easton, Pa., 1906. 

Mulder contended that the organic matter consisted of seven distinct 
compounds, as follows: 1 & 2, Ulmic acid and ulmin; 3 & 4, Humic acid 
and humin; 5, Geic acid; 6, Apocrenic acid; 7, Crenic acid. These 
bodies he considered as arising from one another by oxidation; thus 
ulmic acid (C4„Hi40i2) gave humic acid (C^oHiaOi.,), which in turn yielded 
geic acid (CwHi-O^), followed by apocrenic acid {G^sHi^Ou), and finally 
by crenic acid (C24H12O15). 

'See Schreiner, O., and Shorey, E. C, The Isolation of Harmful Or- 
ganic Substances from Soils; U. S. Dept. Agr., Bur. Soils, Bui. 53, pp. 
15-16, 1909. 



106 NATURE AND PROPERTIES OF SOILS 

dant results, but these were explained for the time being by 
assuming- that the discrepancies occurred because of added 
molecules of water. 

Later investigators, while progressing rather slowly toward 
definite results, did accomplish one thing of importance. They 
threw considerable doubt on the old ideas of the Mulder 
school of chemists. 

One of the men, whose work established beyond a doubt the 
fact that organic matter was a mixture of very complicated 
compounds, was Van Bemraelen.^ His investigations still 
further showed that the soil organic matter was largely in a 
colloidal condition, and, therefore, exhibited properties quite 
distinct from those shown by true solutions or matter in a 
coarse state of division. 

In recent years, Baumann - by his researches has shown 
freshly precipitated organic matter to possess properties which 
are largely colloidal in nature. Among these characteristics 
are high water capacity, great absorptive power for certain 
salts, ready mixture with other colloids, power to decompose 
salts, great shrinkage on drying, and coagulation in the pres- 
ence of electrolytes. Jodidi ^ has studied the composition of 
the acid-soluble organic nitrogen in peat and mineral soils. 
The nitrogenous compounds thus obtained can be divided into 
the following groups: (1) ammoniacal nitrogen, (2) nitric 
nitrogen, (3) acids amides, (4) mon- and diamino-acids. The 
two latter groups * carry the bulk of the organic nitrogen, 

^ Van Bemmelen, J. M., Die Absorptions Verbindungen und das Ab- 
sorptionsvernwgen der Ackererde ; Landw, Versuch. Stat., Band 35, 
Seite 67-136, 1888. 

^Baumann, A., Untersuchungen Tiber die Hummussduren ; Mitt. d. K. 
bayr. Moorkulturanstalt, Heft 3, Seite 53-123, 1909. 

^Jodidi, S. L., Organic Nitrogenous Compounds in Peat Soils I; Mieh. 
Agr. Exp. Sta., Tech. Bui. 4, Nov., 1909. Also, The Chemical Nature of 
the Organic Nitrogen in Soil; la. Agr. Exp. Sta., Ees. Bui. I, June 1911. 

* Amides or acid amides are formed from organic acids by replacing 
the hydro xyl of the earboxyl group with NHj. Acetic acid (CH3COOH) 



THE ORGANIC MATTER OF THE SOIL 107 

but quantitative determinations are uncertain. These com- 
pounds produce ammonia readily, the rate depending on their 
chemical structure. 

The present knowledge of the chemical constitution of the 
soil organic matter is due largely to investigations prosecuted 
by the United States Bureau of Soils.^ As a result of several 
years work a large number of compounds were isolated. Some 
are original constituents of the plant tissue but the bulk has 
arisen through the process of organic decomposition. 

The compounds isolated were classified from the chemical 
standpoint under four heads, those containing: (1) carbon 
and hydrogen; (2) carbon, hydrogen, and oxygen; (3) car- 
bon, hydrogen, and nitrogen, or carbon, hydrogen, oxygen, 
and nitrogen; (4) sulfur in combination with any or all of 
the elements listed above. With the possible presence in 
soils of compounds containing so many elements, it is little 
wonder that the subject is a complicated one. It is evident, 
moreover, that any list now available will be only partial, and 
that many other compounds of even more intricate composi- 
tion will be isolated later. 

A list of some of the compounds isolated from soil organic 
matter by the Bureau of Soils follows: 

thus becomes acet-amide (CHsCONHz). Amino-acids are produced by 
replacing one of the alkyl/hydrogens with NHj. Acetic acid thereby 
becomes amino-acetic acid or glycocoll (CH2(NH2)COOH). Protein/hy- 
drolysis is probably as follows: 

-Acid amides 
Proteins — > Proteoses — > Peptones — > Peptides /^ 

^Amino-acids 

* Sehreiner, O. and Shorey, E. C, The Isolation of Harmful Substances 
from Soils; IT. S. Dept. Agr., Bur. Soils, Bui. 53, 1909; also Buls. 47, 70, 
74, 77, 80, 83, 87, 88, and 90. See also, Sullivan, -M. X., Oripin of 
Vanillin in Soil; Jour. Ind. & Eng. Chem., Vol. 6, No. 11, pp. 919-921, 
1914. Kelley, W. P., The Organic Nitrogen of Hawaiian Soils; Jour. 
Amer. Chem. Soc, Vol. XXXVI, No. 2, pp. 429-444, Feb., 1914. Walters, 
E. H., Proteoses and Peptones in Soils; Jour. Ind. & Eng. Chem., Vol. 
7, No. 10, pp. 860-863, 1915. Lathrop, E. C, Protein Decomposition 
in Soils; Soil Sci., Vol. I, No. 6, pp. 509-532, June, 1916. 



108 NATURE AND PROPERTIES OF SOILS 

Hentriacontane — CsJiei Histidine — C^HpOgNg 

Dihydroxystearic acid — Trithi()ll)eiizaldeliyde — 

C,J1,,0, (C,33CSH)3 

Succinic acid- — CJleO^ Creatinine — C4H.ON3 

Picoline carboxylic acid — Salicylic Aldehyde — 

C.H.O^N C,H,OHCOH 

57. Relation of organic compounds to plants. — So far as 
the plant is concerned, organic compounds may be divided 
into three groups: those that are beneficial, those that are 
neutral, and those that are toxic or harmful in their effects. 
As an example of the first group, histidine and creatinine ^ 
may be mentioned. Here is a case in which the compounds 
in the soil organic matter may exert a stimulating effect on 
plant growth, supplementing the nitrates ^ to a certain extent. 
That the nitrogen of the soil organic matter may be utilized 
by plants is well summarized by the publications of Hutchin- 
son and Miller.^ As an example of a harmful compound aris- 
ing from the decomposition of the organic matter, dihydroxy- 
stearic acid may be mentioned as one of the best known. This 
compound was the first to be isolated and identified by the 
Bureau of Soils and is very toxic. 

The discovery of such compounds in the soil has revived the 
old theory of toxicity,* by which the infertility of certain 
soils was accounted for. Root excretions were also held to be 
detrimental to succeeding crops of the same kind. The toxic 
materials of the soil organic matter largely originate under 

^Skinner, ,J. J., Effect of Histidine and Arginine as Soil Constituents ; 
Eighth Internal. Cong. App. Chem., Vol. XV, pp. 253-264, 1912. Also, 
Beneficial Effects of Creatinine and Creatine on Growth; Bot. Gaz., 
Vol. 54, No. 2, pp. 152-163, 1912. 

^Schreiner, O., and Skinner, .T. ,J., Nitrogenous Soil Constituents and 
Their Bearing upgn Soil Fertility; U. S. Dept. Agr., Bur. Soils, Bui. 87, 
p. 68, 1912. Also, Schreiner, 0., and Others, A Beneficial Organic Con- 
stituent of Soils; Creatinine ; U. S. Dept. Agr., Bur. Soils, Bui. 83, p. 44, 
1911. 

^ Hutchinson, H. B., and Miller, N. H. J., The Direct Assimilation 
of Inorganic and Organic Forms of Nitrogen hi/ Higher Plants; Jour. 
Agr. Sci., Vol. 4, Part 3, pp. 282-302, 1912. 

*See Schreiner, 0., and Eeed, H. S., Some Factors Influencing Soil 
Fertility; U. S. Dept. Agr., Bur. Soils, Bui. 40, pp. 36-40, 1907. 



THE ORGANIC MATTER OF THE SOIL 109 

conditions of poor drainage and aeration. The toxicity of 
such compounds as dihydroxystearie acid, picoline carboxylic 
acid and aldehydes may, therefore, be overcome by oxidation.^ 
Good soil aeration is a factor in dealing with such conditions. 

Fertilizers, according to Schreiner and Skinner,^ seem to 
decrease the harmful effects of such compounds; nitrogenous 
fertilizers overcoming some toxic materials, and phosphoric 
acid or potash neutralizing others. Robbins ^ has shown that 
soil organisms have the power of causing the disappearance 
of certain toxic materials in the soil, such as cumarin, vanillin, 
pyridine, and quinoline. 

While. Schreiner found twenty soils, out of a group of sixty 
taken in eleven states of this country, to contain dihydroxy- 
stearie acid, this does not necessarily mean that this or sim- 
ilar compounds are serious detrimental factors. It is very 
likely that such compounds are merely products of improper 
soil conditions, and are to be considered as concomitant with 
depressed crop yield. When such conditions are righted, the 
so-called toxic matter will disappear, as has been shown by 
the researches of Davidson.* Good drainage, lime, tillage, 
aeration, and oxidation, are so efficacious in this regard that 
permanent organic soil toxicity need never be a factor in soils 
rationally managed, 

^Schreiner, O., and Others, Certain Organic Constituents of Soils in 
delation to Soil Fertility ; U. S. Dept. Agr., Bur. Soils, Bui. 47, p. 52, 
1907. Also, Schreiner, O., and Reed, H. S., The Bole of Oxidation in 
Soil Fertility; U. S. Dept. Agr., Bur. Soils, Bui. .56, p. 52, 1906. 

* Schreiner, O., and Skinner, J. J., Organic Compounds and Fertilizer 
Action; U. S. Dept. Agr., Bur. Soils, Bui. 77, 1911. Also, Experi- 
mental Study of the Effect of Some of the Nitrogenous Soil Constituents 
on Growth; Plant World, Vol. 16, No. 2, pp. 45-60, Feb., 1913. 

' Robbins, W. J., The Cause of the Disappearance of Cum-arin, Vanillin, 
Pyridine and Quinoline in the Soil; Ala. Agr. Exp. Sta., Bui. 195, .June, 
1917. Also, The Destruction of Fa7iillin in the Soil by the Action of 
Soil Bacteria; Ala. Agr. Exp. Sta., Bui. 204, June, 1918. Robbins, W. J., 
and Massey, A. B., Tlie Effect of Certain Environmental Conditions on 
the Bate of Destruction of Fanillin by a Soil Bacterium; Soil Sci., 
Vol. X, No. 3, pp. 237-246, Sept., 1920. 

* Davidson, J., A Comparative Study of the Effects of Cumarin and 
Vanillin on Wheat Grown in Soil, Sand and Water Culture; Jour. 
Amer. Soc. Agron., Vol. 7, No. 4, pp. 145-158, 1915. 



110 NATURE AND PROPERTIES OF SOILS 

58. Simple products of organic decomposition. — As the 

processes of chemical and biological change of the soil organic 
matter proceed, the simple compounds already noted begin 
to appear. This change is of course coordinate with a certain 
amount of synthetic action, but compounds thus built up 
must ultimately succumb to the agencies at work and suffer a 
splitting-up and reduction to simple bodies. Carbon dioxide 
is one of the most important of these compounds, always being 
a product of bacterial activity. Its importance has already 
been noted in the discussion of weathering. Here it heightens 
the solvent power of water and tends to increase the amount of 
nutrient material carried in the soil solution. Carbonation 
is a direct result of its presence. 

With increased organic matter in any soil, greater bacterial 
action and an increase in the carbon dioxide evolved may well 
be expected. In fact, the carbon dioxide production of a 
soil is considered by some authors ^ to be a measure of bacterial 
activity. With this increase in carbon dioxide, the soil air 
is markedly reduced in its free oxygen and an alteration in 
bacterial and plant relationships may thereby be induced. 
The following figures by Wollny ^ show the composition of 
the soil atmosphere and the effects of additional organic ma- 
terial on the carbon dioxide content : 

Table XXI 



Soils 


Percentage by Volume of 




CO, 





Atmospheric air 


.04 
2.54 
1.06 
9.74 


20.96 


Soil air (average 19 analyses) 

A sandy soil 


18.33 
19.72 


Sandy soil plus manure 


10.35 



^Stoklasa, J., and Ernest, A., trher den Ursprung, die Menge, und die 
Bedeutung des KoMendioxyds im Boden; Centrlb. Bakt., II, 14, Seite 
723-736, 1905. 

^Wollny, E., Die Zersetsung der Organischen Stoffe; Seite 2, Heidel- 
berg, 1897. 



THE ORGANIC MATTER OF THE SOIL 111 

While carbon dioxide may be evolved by the splitting-up 
of both carbohydrate and nitrogenous bodies, ammonia re- 
sults only from the latter. It is really the first extremely 
simple nitrogenous body produced. It can be utilized by 
some plants as a source of nitrogen, as is also true of certain 
products of partial decomposition such as urea, but ordinarily 
it must undergo oxidation. This oxidation results in nitrites 
(NO2) and ultimately in nitrates (NO3), the latter usually 
being considered as the chief source of the nitrogen utilized 
by plants. 

Other simple products, such as methane (CH^), hydrogen 
disulphide (HoS), carbon disulphide (CSg), and the like, may 
also result. They are relatively unimportant, however, as 
regards the plant, in comparison with the role played by car- 
bon dioxide, ammonia, the nitrites, and the nitrates. The 
production of the nitrates from ammonia is very closely cor- 
related with good soil conditions, especially optimum moisture 
and adequate aeration. The proper handling of the soil, then, 
will not only tend to eliminate toxic matter and prevent its 
further formation but will encourage the proper decay of the 
soil organic matter and the production of simple compounds 
which will function directly or indirectly as nutrients. 

59. Carbonized materials of soil. — After the extraction 
of the soil for the study of the ordinary organic compounds, 
a considerable mass of material remains, which is insoluble 
in water, alkali, and other ordinary solvents. By the extrac- 
tion of a large amount of soil, Schreiner and Brown ^ were 
able to study this material. They found it susceptible to di- 
vision into six groups, as follows: (1) plant tissue, (2) insect 
and other organized material, (3) charcoal particles, (4) lig- 
nite, (5) coal particles, and (6) materials resembling natural 
hydrocarbons, as bitumen, asphalt, and the like. Such ma- 

* Schreiner, 0., and Brown, B. E., Occurrence and Nature of Carbon- 
ized Material in Soils; U. S. Dept. Agr., Bur. Soils, Bui. 90, 1912. 



112 NATURE AND PROPERTIES OF SOILS 

terial was found not only near the surface of the soil but at 
depths of fifteen or twenty feet. 

The exact origin of this material is problematical. Forest 
and prairie fires, infiltration, mild oxidation, and lignifica- 
tion might be mentioned. Of a certainty the agencies of dis- 
tribution are the natural forces engaged in physical weather- 
ing. Such material can be divided into two general groups, 
organized and unorganized; in the former, the normal struc- 
ture remains intact, while in the latter the original features 
have been obliterated. Part of it belongs, therefore, in the 
original plant tissue group ; a part of it with the partially de- 
cayed material ; while some must be included with the simple 
products of decomposition. This carbonized material is im- 
portant, as it makes up no inconsiderable part of the soil 
organic matter. It is very resistant, and consequently lends 
stability to the organic constituents. 

60. The determination of soil organic matter.^ — A num- 
ber of methods have been proposed for the direct or indirect 
determination of the organic matter in soils, but none has 
proved entirely satisfactory, since the composition of this ma- 
terial is so indefinite and complicated and so likely to change 
while under investigation. Other soil constituents also tend 
to interfere with the determination. Three general methods 
seem worthy of mention, as they have been used very widely 
in soil analyses and at least give comparative, if not absolutely 
accurate, results. They will be discussed in the inverse order 
of their value. 

Loss of ignition.^ — This is a simple method which designs 
to burn off the organic matter and determine its loss by dif- 
ference. Five grams of dry soil are placed in a crucible and 
ignited at a low red heat until the organic matter is all oxi- 

^Soil organic matter as here used refers only to the original and 
partially decayed organic constituents. Carbon dioxide^ methane, nitrites, 
nitrates and similar compounds are, therefore, not included in this term. 

^ Wiley, H. W., Official and Provisional Methods of Analysis; U. S. 
Dept. Agr., Bur. Chem., Bui. 107, p. 19, 1908. 



THE ORGANIC MATTER OF THE SOIL 113 

dized. The cold mass is moistened with ammonium carbonate 
and heated to a temperature of 150°C. in order to expel the 
excess of ammonia and replace the carbon dioxide. The 
change in weight is rated as loss on ignition. 

This method is open to the objection that, besides the loss 
of organic matter, a certain amount of water of combina- 
tion, and all ammoniacal compounds, nitrates, carbon dioxide, 
and some alkali chlorides, if the temperature is carried too 
high, are driven off. The method, therefore, gives high results, 
especially in the presence of large amounts of hydrated sili- 
cates such as are likely to occur in residual soils. Notwith- 
standing these objections, this method has been used to a very 
great extent in soil analysis.^ 

Chromic acid me^/ioc?.— This method, proposed by Wolff, 
has been modified and improved by various chemists. War- 
ington and Peake - have perhaps done more with the method 
than any other investigators. In the United States the modi- 
fication by Cameron and Breazeale ^ has been very generally 
accepted.* It consists in the treatment of the soil sample with 
sulfuric acid, and chromic acid, or potassium bichromate. 
The organic matter, in the presence of the sulfuric acid and 
an oxidizing agent, evolves carbon dioxide until, if the mix- 

* Eather offers a modification to this method which seems to obviate 
some of its difficulties. The soil is first extracted with dilute HCl and 
HF to remove the hydrated aluminum silicates, the organic matter being 
little influenced thereby. The sample is then ignited in the usual 
manner. Rather, J. B., An Accurate Loss-on-Ignition Method for the 
Betermination of Orqanic Matter in Soils; Jour. lud. and Eng. Chem., 
Vol. X, No. 6, pp. 439-442, June, 1918. 

^ Warington, R., and Peake, W. A., On the Betermination of Carbon in 
Soils; Jour. Chem. Soc. (London), Trans., Vol. 37, pp. 617-625, 1880. 

^Briggs, L. J., and others, The Centrifugal Methods of Meclianical 
Soil Analysis; U. S. Dept. Agr., Bur. Soils, Bui. 24, pp. 33-38, 1904. 
Also, Cameron, F. K., and Breazeale, J. F., The Organic Matter in Soils 
and Subsoils; Jour. Amer. Chem. Soc, Vol. 26, pp. 29-45, 1904. 

••Waynick offers a simplification of this method: Waynick, D. D., A 
Simplified Wet CombiLstion Method for the Betermination of Carbon in. 
Soils; Jour. Ind. and Eng. Chem., Vol. XI, No. 7, pp. 634-637, 1919. 



114 NATURE AND PROPERTIES OF SOILS 

ture is boiled, practically all of the carbon is thus driven off. 
This gas is drawn through a train of absorption bulbs, caught 
in a solution of potassium hydroxide, and thus weighed. 

A second determination is now made on a new sample of 
soil, leaving out the chromic acid. The carbon dioxide given 
off under such conditions is that of an inorganic nature. The 
weight of this gas substracted from the total carbon dioxide 
leaves the organic carbon dioxide. 

The data from the use of the chromic acid method may be 
expressed as organic carbon or as organic matter. Multiply- 
ing the carbon dioxide by .471 or the carbon by 1.724 is con- 
sidered as giving an approximate figure for the organic mat- 
ter. 

The results obtained with the chromic acid method are usu- 
ally lower than those from ignition or combustion, due par- 
tially to the oxidation resistance of the carbonized matter, 
already discussed. This material, while it succumbs to igni- 
tion, resists the action of the sulfuric and chromic acids to 
a very large degi'ee. The water of hydration is, of course, not 
a factor in the chromic acid method. 

Bomh Combustion. ^ — Two grams of soil, .75 gram of mag- 
nesium powder, and 10 grams of sodium peroxide (Na^Oa) 
are thoroughly mixed in a closed dry calorimeter bomb. The 
mixture is then exploded by heating, all of the carbon of the 
soil being changed to the carbonate form by the reaction. 
The fused charge is now removed to a flask and by treating 
with acid, the carbon in the form of carbon dioxide may be 
driven off into a Parr apparatus and measured under stand- 
ard conditions of temperature and pressure. 

The amount of inorganic carbonate carbon in the soil must 

^ Wiley, H. W., Official and Provisional Methods of Analysis; U. S. 
Dept. Agr., Bur. Chem., Bui. 107, p. 234, 1908. 

There are a number of other methods of complete combustion. Very 
often the combustion is carried on in a current of oxygen over hot 
cuprous oxide. The organic carbon may thus be very accurately 
determined. 



THE ORGANIC MATTER OF THE SOIL 



115 



be determined on a separate sample and deducted from the 
figure obtained by the combustion above described. This will 
give the organic carbon of the soil in terms of carbon dioxide. 
The percentage of organic carbon may now be calculated as 
well as the approximate amount of organic matter (C X 1.724 
= organic matter or CO2 X -471 := organic matter.)^ 

61. Determination of soil humus. — Humus ^ is a term ap- 
plied to that portion of the organic matter which can be re- 
moved with ammonium hydroxide after the soil has been 
treated with hydrochloric acid and washed free thereof. The 
common method of humus estimation is that proposed by 
Grandeau.^ The sample of soil is first washed with acid in 
order to remove the bases in combination with the organic mat- 
ter. It is next treated with ammonia, which will then dissolve 
out the humous materials. The method is based on the fact 
that when a soil is lacking in active basic material, certain 
parts of the organic matter are soluble in an alkali. The dark 
humous extract obtained with the ammonia is called Matiere 
Noire and is supposed to be the most active part of the soil 
organic matter. 

This method has undergone several modifications * of which 

* Wiley presents the following comparisons of the three methods dis- 
cussed above: 



Soil 


Ignition 


Combustion 
(c X 1.724) 


Chromic acid 
(c X 1.724) 


Old pasture 

New pasture 


9.27 
7.07 
5.95 


6.12 
4.16 

2.44 


4.84 
3.32 


Arable soil 


2.03 







Wiley, H. W., Principles and Practices of Agricultural Analysis, Vol. 
1, pp. 352-354, Easton, Pa., 1906. 

^ The term ' ' humus ' ' is used in a number of different ways. Conti- 
nental Europeans make it synonymous with organic matter. In some cases 
it is used to indicate all of the partially decayed material of the soil. The 
restricted meaning employed in this text is less confusing as it coincides 
with the chemical interpretation. Grandeau believed the organic matter 
thus dissolved was a determining factor in soil fertility. 

"Grandeau, L., Traiti d' Analyse de Matieres Agricoles; I, p. 151, 1897. 

* A comparison of the various methods is found as follows : Alway, 



116 NATURE AND PROPERTIES OF SOILS 

that of Hilgard ^ and that of Houston and McBride - seem 
most important. 

In the procedure an attempt is made to keep the concen- 
tration of the ammonia in contact with the soil constant dur- 
ing the extraction. Consequently the sample, after treatment 
with the acid, is washed into a 500 cubic centimeter flask, 
which is filled to the mark with 4 per cent, ammonia. Diges- 
tion is allowed to proceed for twenty-four hours, with fre- 
quent shakings. The solution is then filtered and evaporated 
to dryness. The residue is weighed, after drying thoroughly 
at 100° C, and then ignited, the loss being considered as 
humus. 

This method is open to serious criticism in that it is wholly 
arbitrary and subject to considerable inaccuracy through 
manipulation and the ignition of the humic residue. There 
is also some doubt whether the figures obtained have any 
direct relation to the fertility of the soil.^ 

62. The organic matter and nitrogen of representative 
soils. — The amount of organic matter in soils varies so widely 
according to the nature of the soil and climate conditions that 
it is difficult to present representative figures. Excluding 
peat and muck, which are 20 to 80 per cent, organic, the aver- 
age mineral surface soil is found to contain from .50 per cent, 
to 18 or 20 per cent, of organic matter. Some surface soils 
of West Virginia,* averaging 2.88 per cent, organic matter, 
F. J., and others, The Determination of Humus; Neb. Agr. Exp. Sta., 
Bui. 115, June, 1910. 

^ Hilgard, E. W., Humus Determination in Soils; U. S. Dept. Agr., 
Div. Chem., Bui. 38 (edited by H. W. Wiley), p. 80, 1893. 

^Houston, H. A., and McBride, F. W., A Modification of Grandeau's 
Method for the Determination of Humus; U. S. Dept. Agr., Div. Chem., 
Bui. 38 (edited by H. W. Wiley), pp. 84-9^, 1893. See also. Smith, O. C, 
A Proposed Modification of the Official Method of Determining Humus; 
Jour. Ind. and Eng. Chem., Vol. 5, No. 1, pp. 35-37, Jan., 1913. 

'Gortner, R. A., The Organic Matter of the Soil; III. On the Pro- 
duction of Humus from Manures; Soil Sci., Vol. Ill, No. 1, pp. 1-8, Jan., 
1917. Carr, R. H., Is the Humus Content of the Soil a Guide to Fer- 
tility; Soil Sci., Vol. Ill, No. 6, pp. 515-524, June, 1917. 

* Salter, E. M., and Wells, C. F., Analyses of West Virginia Soils; 
W. Va. Agr. Exp. Sta., Bui. 168, Dec, 1918. 



THE ORGANIC MATTER OF THE SOIL 117 

range from .73 per cent, to 15.14 per cent., while similar fig- 
ures on the Russian Tschernozen ^ vary from 3.45 to 16.72 
with an average of 8.07 per cent. The subsoil of course runs 
lower in every case. The following figures, while far from 
representative, are suggestive: 

Table XXII 

PERCENTAGE OF ORGANIC MATTER (C X 1.724) IN CERTAIN 
REPRESENTATIVE SOILS OF THE UNITED STATES. 



Description 


Surface 


Subsoil 


8 Residual soils — Robinson - 

3 Glacial and loessial soils — Robin- 
son ^ 


1.76 

4.59 
2.86 
3.83 

7.46 


.64 
144 


2 Kansas till soils Call ^ 

6 Nebraska loess soils — Alway * 

30 Minnesota till soils — Rost and 

Alway ^ 


1.98 
1.96 

1.88 







As the soil nitrogen is carried almost wholly by the organic 
matter, and is a true organic constituent of the soil, its con- 
sideration at this point is opportune. The nitrogen ^ of soils 
varies with the organic matter and may range in surface 
mineral soils from .01 to .60 per cent. West Virginia ^ soils, 

^ Kossowitsch, P., Die Schwarzerde ; Internat. Mitt. f. Bodenkiinde, 
Band I, Heft 3-4, S. 316, 1912. 

^ Robinson, W. O., The Inorganic Composition of Some Important 
American Soils; U. a Dept. Agr., Bui. 122, 1914. 

' Call, L. E., ei al^, Soil Survey of Shawnee County, Kansas; Kans. 
Agr. Exp. Sta., Bui. 200, 1914. 

* Alway, F. J., and McDole, G. R., The Loess Soils of the NeirasTca 
Portion of the Transition Region: I. Hygroscopiciti/, Nitrogen and 
Organic Carbon; Soil Sei., Vol. I, No. 3, pp. 197-238, Mar., 1916. 

° Rost., C. O., and Alway, F. J., Minnesota Glacial Soil Studies; I. A 
Comparison of the Soils of the Late Wisconsin and lowan Drifts; 
Soil Sci., Vol. XI, No. 3, pp. 161-200, Mar., 1921. 

*Soil nitrogen is determined by either the Kjeldahl or the Gunning 
method. These will be described later. See paragraph 165. 

'Salter, R. M., and Wells, C. F., Analyses of West Virginia Soils; 
W. Va. Agr. Exp. Sta., Bui. 168, Dec, 1918. 



118 NATURE AND PROPERTIES OF SOILS 

for example, while averaging .147 per cent, nitrogen, range 
from .043 to .539. Louisiana ^ soils average .049 per cent, with 
a range from .001 to .109. In muck and peat the amount of 
nitrogen is much higher, attaining in some cases 3 per cent. 

The following figures indicate the nitrogen contents that 
may be expected in average soils: 

Table XXIII 

PERCENTAGE OF NITROGEN IN CERTAIN REPRESENTATIVE SOILS 
OF THE UNITED STATES 



Description 


Soil 


Subsoil 


71 Cecil soils of North Carolina - . . . . 
165 Norfolk soils of North Carolina ^. . 

16 Loess soils of Central U. S.* 

381 Kentucky soils ^ 


.048 
.039 
.154 
.120 
.338 


.024 
.020 
.083 
.070 


30 Minnesota till soils ^ 


.092 







While the ratio between the respective amounts of soil 
nitrogen and organic' matter is no more constant than that 
between the organic carbon and the organic matter 
(C X 1.724 = organic matter), it is of some general value. If 

^ Walker, S. S., Chemical Composition of Some Louisiana Soils as to 
Series and Texture; La. Agr. Exp. Sta., Bui. 177, Aug., 1920. 

^Williams, C. B., et at., Beport on the Piedmont Soils, Particularly 
with Beference to their Nature, Plant-food Requirements and Adaptor 
bility to Different Crops; Bui. N. C. Dept. Agr., Vol. 36, No. 2, Feb., 
1915. 

^Williams, C. B., et al., Beport on Coastal Plain Soils, Particularly 
with Beference to their Nature, Plant-food Bequirements and Suitability 
for Different Crops; Bui. N. C. Dept. Agr., Vol. 39, No. 5, May, 1918. 

*Eobinson, W. O., et al., Variation in the Chemical Composition of 
Soils; U. S. Dept. Agr., Bui. 551, June, 1917. Alway, F. J., and McDole, 
G. E., The Loess Soils of the Nebraska Portion of the Transition Re- 
gion: I. Hygroscopicity, Nitrogen and Organic Carbon; Soil Sei., 
Vol. I, No. "3, pp. 197-238, Mar., 1916. Also, Bennett, H. H., Soils and 
Agriculture of the Southern States, pp. 332-353 ; New York, 1921. 

" Averitt, S. D., The Soils of Kentucky; Ky. Agr. Exp. Sta., Bui. 193, 
July, 1915. 

"Eost, C. O., and Alway, F. J., Minnesota Glacial Soil Studies: I. A 
Compariso7i of the Soils of the Late Wisconsin and the loivan Drifts; 
Soil Sci., Vol. XI, No. 3, pp. 161-200, Mar., 1921. 



THE ORGANIC MATTER OF THE SOIL 



119 



the percentage of nitrogen in the soil is multiplied by 20, a 
rough idea of the amount of organic matter may be obtained 
(N X 20 == organic matter). The following data from Rost 
and Alway ^ illustrate not only the variations in organic 
matter and nitrogen that may be expected in the surface and 
subsurface of different soils, but the correlation between the 
organic matter and nitrogen just mentioned: 

Table XXIV 

AVERAGE PERCENTAGE OF ORGANIC MATTER (C X 1.724) AND 

NITROGEN IN THIRTY REPRESENTATIVE MINNESOTA TILL SOILS 

FROM THREE SERIES. THE FIGURES FOR EACH OF THE 

THREE SOIL TYPES ARE AVERAGES OF TEN ANALYSES. 



Dkpth 


Forest 

Carrington 

Loam 


Upland Prairie 

Carrington Silt 

Loam 


Lowland 

Prairie 

Fargo Silt Loam 




Organic 
Matter 


Nitro- 
gen 


Organic 
Matter 


Nitro- 
gen 


Organic 
Matter 


Nitro- 
gen 


1 — 6 inches. . . 

7—12 " 

13 24 " 

25 36 '' 


5.34 

2.41 

1.38 

.86 


.253 
.119 

.078 
.041 


7.96 
6.00 
S.ll 
1.31 


.373 

.285 
.165 
.062 


13.08 
8.00 
3.24 
1.39 


.616 
.385 
.150 
.054 



The following tentative classification of mineral soils on the 
basis of their percentages of organic matter and nitrogen is 
offered for generalized field use : 



Table XXV 



Description 


Percentage of 
Organic Matter 


Percentage op 
Nitrogen 


Low 


.0— 3.0 

3.0— 6.0 

6.0 10.0 

above 10.0 


00— 10 


Medium 

High 


.10— .25 
25 40 


Very high 


above .40 



^ Rost, C. O., and Alway, F. J., Minnesota Glacial Soil Studies: I. A 
Comparison of the Soils of the Late Wisconsin and the lotvan Drifts; 
Soil Sci., Vol. XI, No. 3, pp. 161-200, Mar., 1921. 



120 



NATURE AND PROPERTIES OF SOILS 



63. The humus content of soils is of com-se lower than 
the organic matter contained in them. It likewise varies 
according to climate and region, not only in amount, but also 
in composition. The following data from Hilgard ^ and 
Alway - illustrate these points : 

Table XXVI 

THE COMPOSITION OF CALIFORNIA ARID AND HUMID SOILS. 



(hilgard) 






Description 


Humus in 
Soil 

(Percentage) 


Nitrogen in 

Humus 
(Percentage) 


Nitrogen in 

Soil 
(Percentage) 


41 Arid uplands soils 

15 Sub irrigated arid soils. . 
24 Humid soils 


.91 
1.06 

4.58 


15.23 

8.38 
4.23 


.135 
.099 
.166 







Table XXVII 

COMPARATIVE COMPOSITION OF SEMI-ARID (wAUNETA) AND HUMID 
(weeping water) LOESS SOILS OF NEBRASKA. ( ALWAY ) 





Organic Matter 
(Percentage) 


Humus 
(Percentage) 


Nitrogen 
(Percentage) 




Wauneta 


Weeping 

Water 


Wauneta 


Weeping 
Water 


Wauneta 


Weeping 
Water 


1st foot. 
2nd ".. 
3rd "... 
4th "... 
5th "... 
6th "... 


2.77 

1.38 

1.09 

.79 

.55 

.45 


4.98 

3.02 

1.38 

.83 

.45 

.36 


1.02 
.65 
.48 
.34 
.26 
.26 


2.34 

1.29 

.55 

.27 
.23 
.19 


.136 
M2 
.065 
.046 
.038 
.030 


.236 
.154 
.083 
.059 
.043 
.038 



^Hilgard, E. W., Soils, pp. 136-137; New York, 1911. For further 
data regarding Hilgard 's conclusions see: Alway, F. J., and Bishop, 
E. S., Nitrogen Content of the Humus of Arid Soils; Jour. Agr. Pies., 
Vol. 5, No. 20, pp. 909-916, Feb., 1916. 

' Alway, F. J., et ah, The Loess Soils of the Nebraska Portion of the 
Transition Becjion: I. Hygroscopicity, Nitrogen and Organic Carbon; 
Soil Sci., Vol. I, No. 3, pp\ 197-238, Mar., 1916. //. Humus, Humus-Ni- 
trogen and Color; Soil Sci., Vol. I, No. 3, pp. 239-258, Mar., 1916. 



THE ORGANIC MATTER OF THE SOIL 121 

It is eviden«t that Immid soils not only contain the greater 
amounts of organic matter, but also excel in humus. The 
humus of the arid regions, however, is richer in nitrogen, due 
to the character of the decomposition going on. As a conse- 
quence the nitrogen in the soil of humid regions is not greatly 
in excess of that in the soils of drier climates. The percentage 
of humus not only decreases in the lower depths of the soil, 
but also changes in composition, becoming poorer in nitrogen 
the deeper the soil. 

64. The influence of organic matter on the soil. — The 
effects of organic matter on soil and plant conditions are as 
numerous as they are complex. Some of the influences are 
direct, others are indirect. As the specific gravity of organic 
matter is low, the first effect of its addition would be to lower 
the specific gravity of the soil. The organic matter tends also 
to spread the individual particles of soil farther apart, especi- 
ally in a clay. Such action will markedly influence the volume 
weight. 

The loosening effects of organic matter are especially ap- 
parent in such soil as clay* On the other hand, because or- 
ganic matter has a higher cohesive and adhesive power than 
sand, it performs the function of a binding material with the 
latter soil, a condition much to be desired in a material pos- 
sessing such loose structure. 

As the water capacity of organic matter is very high, a soil 
rich in organic constituents usually possesses a high water- 
holding power. This makes possible greater volume changes 
both on drying and in the presence of excessive moisture. The 
granulating effects of wetting and drying and freezing and 
thawing are, therefore, accelerated. The increased water ca- 
pacity of the soil, resulting from the presence of organic ma- 
terials, is of great importance in drought resistance, while 
the black color imparted by the humus tends to raise the 
heat absorptive, power of the soil. 

The better tilth induced by the presence of organic matter 



122 NATURE AND PROPERTIES OF SOILS 

in any soil tends to facilitate ease in drainage and to encour- 
age good aeration. These two conditions are of course neces- 
sary for the promotion of soil sanitation. Root extension and 
bacterial activity are thus increased. It is of especial impor- 
tance that the splitting-up of the organic matter shall take 
place in the presence of plenty of oxygen, in order that toxic 
compounds may not be generated and that products highly 
favorable to plant growth should be formed. 

The soil organic matter, however, functions in other ways 
than those strictly physical and chemical. Its degradation 
products may serve as nutrients for higher plants. Bacteria 
and other soil organisms are also furnished a source of energy 
thereby and the production of carbon dioxide is much in- 
creased. This carbon dioxide, as well as the organic acids 
generated, tends to raise the capacity of the soil-water as 
a solvent, and thus the amount of mineral material available 
to the crop is greatly increased. The general effect of organic 
matter, then, is to better the soil as a foothold for plants, and 
to increase either directly or indirectly the available nutri- 
ent supply for the crop. 

65. Maintenance of soil orgunic matter.^ — The mainte- 
nance of a proper supply of organic matter in a soil is a ques- 
tion of great practical importance, as productivity is gov- 
erned very largely by the organic content of the soil. This 
maintenance of the soil organic matter depends on two factors : 
(1) the source of supply and methods of addition; and (2) 
the promotion of proper soil conditions in order that the 

^Snyder, H., Effect of the Rotation of Crops upon the Humus Content 
and the Fertility of Soils; Minn. Agr. Exp. Sta. Bui. 53, June, 
1897. The Production of Humus in Soils; Minn. Agr. Exp. Sta., Bui. 
89, Jan., 1905. Morse, F. W., Humus in New Hampshire Soils; N. H. 
Agr. Exp. Sta., Bui. 138, .June, 1908. Hopkins, C. G., Phosphorus and 
Humus in Relation to Illinois Soils; 111. Agr. Exp. Sta., Cire. 116. Feb., 
1908. Thatcher, R. W., The Nitrogen and Humus Problem of Dry 
Farming; Wash. Agr. Exp. Sta., Bui. 105, June, 1912. Fippin, E. O., 
Nature, Effects and Maintenance of Humus in the Soil; Cornell Reading 
Course for the Farm, Vol. Ill, No. 50, Oct., 1913. Loughridge, R. H., 
Humus of California Soils; Calif. Agr. Exp. Sta., Bui. 242, Jan., 1914. 



THE ORGANIC MATTER OF THE SOHj 123 

organic matter may perform its legitimate functions. The 
source of supply will be considered first. 

The organic matter of the soil may be increased in a nat- 
ural way by the plowing under of green crops. This is 
called green-manuring and is a very satisfactory practice. 
Such crops as rye, buckwheat, clover, peas, beans, and vetch 
lend themselves to this method of soil improvement. Not 
only do these crops increase the actual organic content of 
a soil, but in the case of legumes the nitrogen may also be in- 
creased in amount, if the nodule bacteria are present and 
active. 

Green-manures to be effective must be hardy, rapid in 
growth, succulent, and should produce abundant foliage. Rye 
and oats are particularly valuable from this standpoint. Such 
legumes as cowpeas, vetch, field peas, soybeans, and velvet 
beans are adapted to summer growth. Red clover or sweet 
clover, being a biennial, may be seeded one year and turned 
under the next spring. Oats and peas or rye and peas make 
a very good combination for fall green-manuring. Hairy or 
winter vetch may be seeded with rye in the autumn and used 
as a green-manure in the spring. In the South green-manur- 
ing crops may be utilized to much better advantage than in the 
northern states as the longer growing season permits the use 
of a green-manure following the normal harvest. 

Due to the tendency of bare soil to lose nutrients by leach- 
ing, especially in the summer and fall, it is always best to 
keep the land covered with vegetation of some kind. Cover- or 
catch-crops are used for this purpose, especially on sandy land, 
although they are profitable on heavier soils as well. Wheat 
on sandy land may be followed by cowpeas, which not only 
conserve nitrates but fix nitrogen from the air in addition. 
Rape, cowpeas, vetch, and soybeans are sometimes seeded in 
com at the last cultivation. When a soil receives clean culti- 
vation a part of the year, as is practiced very frequently in 
orchards, it is very desirable that a crop be plowed under oe- 



124 NATURE AND PROPERTIES OF SOILS 

casionally to replace the organic matter lost by oxidation. 
Whether such catch-crops are pastured or turned under, they 
tend to increase the soil organic matter. Weeds, which spring 
up after the crop is harvested, are often valuable as cover- 
and catch-crops and when turned imder aid in maintaining 
the organic content of the land. 

Crop residues form no inconsiderable portion of the organic 
matter produced on the land. If such materials as straw, 
stubble, cornstalks, and the like are incorporated in the soil, 
much will be accomplished towards the upkeep of the organic 
matter. The burning of straw and cornstalks, especially in 
the Middle West, entails an enormous waste of carbon as well 
as of nitrogen. The value of crop residues has been demon- 
strated very conclusively by the Illinois Experiment Station ^ 
on their outlying experimental farms. At Bloomington, for 
instance, the turning under of crop residues for five years 
increased the wheat yields 4.4, 7.9 and 5.9 bushels in 1911, 
1912 and 1913 respectively. 

Farm manure is one of the most important by-products on 
the farm and is especially valuable because of its organic mat- 
ter. Although only about one-fourth of the organic materials 
of the original food given the animal ever reaches the land, 
the use of such a by-product is worth while, since the carbon 
it contains comes from the air and not from the soil. The main 
losses that the carbon of the crop undergoes when thus util- 
ized are due to the digestive influences of the animal and to 
the leaching and fermentation which goes on in the manure. 
While sufficient manure ordinarily can not be produced from 
the crops grown on the farm to maintain the organic matter 
of its soil, the use of farm manure with green-manure and crop 
residues in a proper rotation is fundamental in good soil man- 
agement. 

66. Organic matter and soil conditions. — Improper soil 

'Hosier, J. G., and Gustafson, A. F., Soil Physics and Management, 
p. 171; Philadelphia and London, 1917. 



THE ORGANIC MATTER OF THE SOIL 



125 



conditions not only prevent tlie proper decay of organic mat- 
ter, but also tend to encourage the production of products in- 
imical to plant growth. Therefore, in order that organic ma- 
terials added to any soil may produce the proper decomposi- 
tion products and perform their normal functions, soil con- 
ditions in general must be of the best. Tile drainage should 
be installed, if necessary, in order to promote aeration and 



50% LOSS 

ORGANIC 
MATTER 




Fig. 22.— Diagram showing tlie practical sources of the soil organic 
matter and the cycle through which its constituents pass. Note 
that the carbon, oxygen and hydrogen come very largely from air 
and water and that fixation of nitrogen may occur if the crop is 
a legume. Only about 25 per cent, of the organic matter fed to 
animals ever reaches the soil in farm manure under average con- 
ditions. 



granulation. Lime should be added if basic materials are 
lacking, for it promotes bacterial activity as well as plant 
growth. The addition of fertilizers will often be a benefit, 
as will also the establishment of a suitable rotation. The 
rotation of crops not only prevents the accumulation of toxic 
materials, but also, by increasing crop growth, makes pos- 
sible a larger addition of organic matter by green-manuring. 



126 NATURE AND PROPERTIES OF SOILS 

67. Resume. — An understanding of the complex organic 
relationships witliin the soil is of great practical value, as 
it determines to a large degree the yield of crops, their rota- 
tion order and their fertilization. Moreover, tillage operations 
must be varied according to the organic nature of the soil. 
Unless a system of soil management is adopted which will at 
least partially keep up the organic matter of the soil, crop 
yields may be expected to decrease materially in a few years. 

Good soil management seeks to adjust the addition of or- 
ganic matter, the physical and chemical condition of the soil, 
and the losses through cropping and leaching, in such a way 
that paying crops may be harvested while impairing the or- 
ganic supply of the soil as little as possible. Any system of 
agriculture that tends permanently to lower the organic mat- 
ter of the land is impractical and improvident, as well as un- 
scientific. 



CHAPTER VI 
THE COLLOIDAL MATTER OF THE SOIL^ 

Research in physics and physical chemistry is each day 
making it clearer that the properties of matter are by no 
means entirely determined by chemical composition. Matter 
varies in its physical character and its chemical activities with 
its fineness of division. Coarsely divided substances function 
much differently when they become molecular complexes and 
still more diversely when their aggregates are divided into 
their molecular and ionic components. Because of the par- 
ticular properties exhibited by material in a fine state of di- 
vision, approaching but not attaining a molecular simplifica- 
tion, a special name is utilized. A substance in such a con- 
dition is said to be colloidal or in the colloidal state. 

68. The colloidal state - arises when one form of matter 
(either a gas, liquid, or solid) in a very fine state of division 

^ Colloidal chemistry is now so well understood that it will be necessary 
to develop only those phases which have a direct bearing on soil 
phenomena. 

^Sonie of the following general references may prove helpful: 

Eamann, E., Kolloidstudien bei Bodenlundlichen Arbeiten; Kolloid- 
chemische Beihef te ; Band II, Heft 8/9, Seite 285-303, 1911. 

Niklas, H., Die Kolloidchemie und Hire Bedeutung filr Bodenlcunde, 
Gcologie, und Mineralogie ; Internat. Mitt, fiir Bodenkunde, Band II, 
Heft 5, Seite 383-403, 1913. 

Bancroft, W. D., The Theory of Colloid Chemistry ; Jour. Phys. Chem., 
Vol. 18, No. 7, pp. 549-558, 1914. 

Taylor, W. W., The Chemistry of Colloids; New York, 1915. 

Burton, E. F., The Physical Properties of Colloidal Solutions; London, 
1916. 

Zsigmondy, E,, The Chemistry of Colloids, Part I; trans, by E. B. 
Spear, New York, 1917. 

Wiegner, G., Boden und Bodenbildung ; Dresden and Leipzig, 1918. 

Bancroft, W. D., Applied Colloidal Chemistri/ ; New York, 1921. 

Thatcher, E. W., Chemistry of Plant Life; Chap. XV, New York, 1921. 

127 



128 NATURE AND PROPERTIES OF SOILS 

is distributed through a second, which may also be a gas, a 
liquid, or a solid. The material in the finely divided state 
is called the dispersed phase, while the matter containing it 
is designated as the continuous or dispersive medium. A 
very good example of a colloidal system occurs when very 
fine clay particles (solids) are suspended in water (liquid) 
or when an emulsion of oil and water is formed, the oil under 
certain conditions becoming the dispersed material, hetero- 
geneously disposed. The particles of material in a colloidal 
state in these cases are so small that they will not sink as long 
as conditions are stable. Moreover, they exhibit the Brownian 
movement,^ the oscillations increasing very rapidly as the 
size decreases. Such particles are molecular complexes and 
the solution is heterogeneous. In this respect a colloidal solu- 
tion differs from a true solution, which is homogeneous, the 
particles being molecules and often ions. 

69. Size of colloidal particles. — The size of the particles 
of matter in a colloidal state vary with the material and with 
the conditions of formation. The diameters of material in a 
colloidal state are considered to range from 100 |i [i ^ (.0001 
m.m.) to 1 n fx (.000001 m.m.). Above 100 \x \i suspended 
material is usually sinkable, while below 1 |i [x the particles 
generally become single molecules and a true solution is at- 
tained. Theoretically it would seem possible to pass from 
a suspension to a true solution without a break by a progres- 
sive subdivision of particles. There seems to be a discontinu- 
ity, however, between the colloidal state and a true solution. 
As the molecular complexes subdivide, they at last go into 
solution and may reprecipitate as coarser complexes, thus 

^ Small particles, even those well within the range of ordinary micro- 
scopic vision, exhibit, when suspended in a liquid, an oscillating motion 
around a central position. This movement^ which is called the Brownian, 
is inversely proportional to the size of the particle. It is probably due 
to the bombardment of the molecules and ions of the liquid in which 
the particle is suspended. The Brownian movement is very slow for 
particles of a diameter of .001 mm. 

^A micron (/i) = .001 mm. or 10-^ mm. A millimicron (liU/t)=: 
.000001mm. or 10* mm. 



THE COLLOIDAL MATTER OF THE SOIL 129 

maintaining a considerable gap between the two states of 
matter.^ 

70. The phases of a colloidal state. — As already empha- 
sized, two phases are necessary for a colloidal state — a dis- 
persive medium and a material that will heterogeneously 
disperse therein. Threee materials may function as a dis- 
persive medium — a liquid, a solid, or a gas. In the same way, 
with each dispersed material there are three possibilities — 
a liquid, a solid, or a gas. This gives eight general phases 
to be considered in colloidal chemistry.^ 

The liquid-solid and the liquid-liquid phases are by far 
the most important as far as soil materials are concerned. 
The dispersed materials of soil colloids are the minerals either 
in a hydrous or non-hydrous condition and the organic mat- 
ter in various stages of decay. The dispersive medium is of 
course the soil solution. 

71. Colloids vs. crystalloids. — It must not be inferred, 
because the colloidal state is often wrongly contrasted with 
the crystalloidal, that material in a colloidal condition is al- 
ways amorphous. It is often crystalline. Moreover, it may be 
animate, as some bacteria are minute enough to function col- 
loidally. It is obvious also that the same chemical material 
may exist either in the colloidal or non-colloidal state. For 
example, silicic acid, hydrated ferric oxide, gold, carbon black, 

•Bancroft, W. D., Applied Colloidal Chemistry, p. 18.3; New York 
1921. 
' The eight phases with examples are : 

Solid in solid Carbon in steel. 

Liquid in solid water of crystallization 

Gas in solid gases in minerals 

Solid in liquid colloidal solution of metals 

Liquid in liquid emulsions of oil in water 

Gas in liquid air in water, foam 

Solid in gas smoke in air 

Liquid in gas clouds 

Gas in gas noncolloidal, merely a mixture of 

molecules. 
After Burton, E. F., The Physical Properties of Colloidal Solutions, 
p. 10; London, 1916. 



130 NATURE AND PROPERTIES OF SOILS 

and other materials, may or may not be colloidal, according 
to circumstances. The fineness of division is the explanation 
of colloidal properties. In order to place such a discussion on 
a more understandable basis, a few additional illustrations 
may not be amiss. The following materials, which may exist 
in a colloidal condition, are for convenience grouped under 
two general heads, organic and inorganic : 

Organic : Gelatin, agar, caramel, albumin, starch jelly, 
humus, some bacteria, carbon black, and tannic acid. 

Inorganic : Gold, silver, hydrated ferric oxide, arsenious 
sulphide, zinc oxide, silver iodide, Prussian blue, and the like. 

72. The properties of colloidal materials. — In general, 
there are certain properties which materials in a colloidal 
state exhibit and by which they are distinguished from true 
solutions. In the first place, since they are not in true solu- 
tion, they exert little or no effect on the freezing point and 
the vapor pressure of liquids. Some colloids have absolutely 
no effect on these properties, while others, as they allow a 
certain small amount of true solution to take place, do possess 
such influences to a slight degree. Secondly, colloids do not 
pass readily through semi-permeable membranes, such as 
parchment paper or pig's bladder. Their diffusive powers 
are low. This serves as an easy way of separating colloidal 
and non-colloidal material. Thirdly, heat and the addition 
of electrolytes will serve to coagulate certain colloids, a prop- 
erty which again serves to distinguish them sharply from a 
true solution. Fourthly, colloidal material has great ab- 
sorptive power, not only for water, but also for gases and 
materials in solution, a quality of extreme importance in soil 
phenomena. 

Many colloids are coagulated by the addition of an elec- 
trolyte,^ the phenomenon often being spoken of as floccula- 

^ An electrolyte is any substance which has the ability when in solution 
to carry an electric current, the substance suffering decomposition there- 
by. The current is carried by the liberated ions. Hydrochloric acid, 
for example, dissociates into ionic hydrogen and ionic chlorine, the 



THE COLLOIDAL MATTER OF THE SOIL 131 

tion.^ A very good example is afforded by treating a colloidal 
clay suspension with a little calcium hydroxide. The tiny 
particles almost immediately coalesce into floccules, and be- 
cause of their combined weight, sink to the bottom of the 
containing vessel, leaving the supernatant liquid clear. The 
same action will take place in the soil itself, but of course with 
less rapidity and under conditions less noticeable to the eye. 
Some dispersed materials, when thus separated from their 
dispersive medium, will reassume the colloidal state with 
ease when an opportunity is offered. In other cases, the col- 
loidal condition is difficult to restore. Gelatin is an example 
of the first group and is called a reversible colloid. Ferric 
hydrate is an example of the more or less irreversible type. 

Just why this phenomenon of flocculation or agglutination 
takes place is rather difficult to state. It is found that cer- 
tain colloids, when subjected to the proper electric current, 
will migrate to either the positive (anode) or the negative 
(cathode) pole. These particles evidently carry a charge of 
electricity. Hydrated ferric oxide, aluminium hydrate, and 
basic dyes, for example, move toward the cathode and carry 
a positive charge; while arsenious sulphide, silicic acid, gold, 
silver, humus and acid dyes move toward the anode and are 
negative. It is assumed that as long as the colloidal particles 
remain charged, they repel each other and the colloidal state 
persists. When an electrolyte is added, which develops by 
ionization a dominant opposite charge, it is supposed to cause 
a neutralization of the repellent electricity carried by the 
colloidal particles, and flocculation occurs. 

Certain colloids may flocculate certain others, as the gela- 

tinization of silic acid by hydrated ferric oxide. At times 

one colloid may protect another, probably by surrounding it 

former carrying a positive and the latter a negative charge of electricity 
(H*-i-C-). KNO3 gives K*+ NO3-. The ionization varies with the 
substance, the dilution and certain other conditions. 

*See Wolkoflf, M. I., Flocculation of Soil Colloidal Solutions; Soil 
Sci., Vol. I, No. 6, pp. 585-601, June, 1916. A good bibliography is 
appended. 



132 NATURE AND PROPERTIES OF SOILS 

with a protective film. Such a case may be shown by adding 
gelatin to a clay suspension. When a colloid such as hy- 
drated ferric oxide is flocculated, it loses to a certain extent 
its colloidal properties, and assumes the characteristics of 
non-colloidal materials. 

73. Soil colloids and their generation.^ — In soils there 
seem to exist two very general and indefinite groups of col- 
loidal materials, besides all gradations and variations: (1) vis- 
cous, gelatinizing and reversible colloids, and (2) non-viscous, 
non-gelatinizing, easily coagulable and irreversible colloidal 
matter. The decaying organic materials in the soil and the 
mineral matter contribute liberally to both groups. Both 
of these groups, with their bewildering variations and grada- 
tions, play important parts in the physical and chemical phe- 
nomena of the normal soil. 

The organic colloidal matter in a soil rich in decomposing 
tissue is obviously of great importance. Such material is very 
heterogeneous, very complex, and constantly changing. As 
yet very little study of the organic soil colloids has been made 
because of the difficulties presented by the problem. Humus 
colloids may be viscous or non-viscous, as the case may be, 
and may or may not be thrown down by calcium hy- 
droxide. The absorptive power of these colloids for water, 
gases, and such materials as calcium, magnesium, and potas- 
sium is very highly developed — as much so, probably, as that 
of the inorganic colloids. These organic colloids are not only 
added as a part of the original plant tissue but are also 
formed during the tearing-down and splitting-off processes 

^Van Bemmelen, J. M., Bis Absorption; Seite 114-115, Dresden, 1910. 
Also, Die Absorptionsverhindungen und das Absorptsvermogen der 
Ackererde; Landw. Ver. Stat., Band. 35, Seite 69-136, 1888 ; Way, J. T., 
On Deposits of Soluble or Gelatinous Silica in the Lower Beds of the 
Chalk Formation; Jour. Chem. Soc, Vol. 6, pp. 102-106, 1854. War- 
ington, R., On tJi,e Fart Taken by Oxide of Iron and Alumina in the 
Adsorptive Action of Soils; Jour. Chem. Soc, 2d ser.. Vol. 6, pp. 1-19, 
1868. Cushman, A. S., The Colloid Theory of Flasticity; Trans. Amer. 
Cer. Soc, Vol. 6, pp. 65-78, 1904. Ashley, H. E., The Colloid Matter 
of Clay and its Measurements ; U. S. Geol. Survey, Bui. 388, 1909. 



THE COLLOIDAL MATTER OF THE SOIL 133 

incident to bacterial activity, during which, compounds are 
thrown off in such a state of division as to assume the condi- 
tion that has been designated as colloidal. Of course the chem- 
ical forces of weathering are also operative in this process of 
organic colloidal production. 

While some inorganic soil colloids, as silicic acid and hy- 
drated ferric oxide, are rather simple chemically, most of 
the mineral colloidal material is extremely complex. The soil, 
especially when of a clayey nature, always contains large 
amounts of complicated hydrated aluminum silicates of con- 
stantly varying constitution.^ Such material, whether simple 
or complex, arises from ordinary weathering reactions and 
develops in the soil as the latter is built up. A simple ex- 
ample may be cited. When a feldspar undergoes decomposi- 
tion the following reaction may be used to illustrate the pos- 
sible change that takes place : 

2KAlSi308 + 2H2O + CO2 = H.ALSi^Oo + 4SiOo + KXOg 

Orthoclase Water Carbon Kaolinite Silica Potassium 

Dioxide Carbonate 

Kaolin almost always originates in this w^ay, an alkali car- 
bonate and silica being formed at the same time. The proc- 
ess is essentially one of hydration and carbonation ; the car- 
bon dioxide by reacting with the alkali permits the process to 
go on. The silica may go to one or more of three possible 
destinations, according to conditions, — to free quartz, to col- 
loidal silica or to make up complex colloidal hydrated alu- 
minum silicates. The last mentioned condition seems the most 

^ The Bureau of Soils have prepared a colloidal solution from soil 
by passing a well shaken mixture of soil and water through a Sharpies 
centrifuge. The colloidal matter was separated from its dispersive 
medium by means of a porcelain filter. This ultra-clay seemed to be 
a mixture of various colloids and consisted mainly of hydrated alu- 
minum silicates with varying amounts of ferric hydroxide, silicic acid, 
organic matter and possiblj^ aluminum hydroxide. 

Moore, C. J., Fry, W. H., and Middleton, H. E., Methods for Deter- 
mining tJie Amounts of Colloidal Material in Soils; Jour. Ind. ami 
Eng. Chem., Vol. 13, No. 6, pp. 527-530, June, 1921. 



134 NATURE AND PROPERTIES OF SOILS 

probable fate of the silica as the process is strongly one of 
hydration. 

74. Influence of colloidal material ^ on soil properties. — 

^ The amount of matter in a colloidal state in soils is extremely 
variable, ranging from almost nothing in sand to a very large percentage 
in heavy plastic clays. There is no satisfactory means of finding the 
amount of colloidal material in soil. All of the available methods depend 
for their expression on the intensity of certain qualities, supposed to 
be developed by colloid content. This indicates that the methods are 
largely comparative rather than exact or strictly analytical in nature. 

Ashley's method depends on the absorption of certain dyes to indicate 
the relative amount of material in a colloidal state. The difficulty in this 
method, however, lies in choosing the most effective dye and regulating 
its concentration. Moreover, different colloids vary so much in absorp- 
tive capacity for the same dye, that only roughly comparative results 
have thus far been possible. 

Mitscherlich uses the absorptive capacity of the soil for water vapor 
as a colloidal index. In this method the air-dry soil in a thin layer is 
brought to absolute dryness over phosphorus pentoxide. It is then 
placed in a desiccator over a 10 per cent, solution of sulfuric acid and 
the condensation is hastened by a partial vacuum. The sulfuric acid 
is used in order to prevent the deposition of dew on tlie soil. After 
exposure for about twenty-four hours, the soils are found to have taken 
up their maximum moisture of condensation, which is called the hygro- 
scopic water. The soil is then weighed, and the increase, figured to a 
percentage based on dry soil, is taken as a measure of colloidal content. 
The reverse process may also be followed, by exposing air-dry soil in a 
saturated atmosphere and afterwards drying over phosphorus pentoxide. 
The hygroscopicity of the soil, or its hygroscopic coefficient, is thus the 
basis for colloidal comparison. 

Ashley, H. E., The Colloid Matter of Clay and Its Measurement; 
U. S. Geol. Survey, Bui. .388, 1909. 

Eodewald, H., und Mitscherlich, A. E., Die Bestimmung der Hygro- 
sliopisitdt; Landw. Ver. Stat., Band 59, Seite 433-441, 1903. Also, 
Mitscherlich, E. A., und Ploess, R., Ein Beitrage sur Bestimmung der 
Eygrosl'opizitdt und zur Bewertung der physikolischen Bodenanalyse; 
Internat. Mitt. f. Bodenkunde, Band 1, Heft 5, Seite 463-480, 1912. 

Ehrenberg, P., und Pick, H., Beitrage sur Physilcalischen Bodenunter- 
suchung ; Zeit. f. Forst- und Jagdwesen, Band 43, Seite 35-47, 1911. 
Also, Vageler, P., Die Bodewald-Mitscherliclische TJieorie der Hygro- 
skopizitdt vom Standpunkte der Colloidchemie und ihr Wert sur Beur- 
teitung der Boden; Fuhling's Landw. Zeit., Band 61, Heft 3, Seite 73-83, 
1912. 

Stremme, H., and Aarnio, B., Die Bestimmung des Gehaltes anorga/n- 
ischer Kolloide in Zersetzten Gesteinen und deren tonigen TJnlagerungs- 
produkten; Zeitsch. f. Prak. Geol., Band 19, Seite 329-349, 1911. 

Tempany, H. A., Shrinkage in Soils; Jour. Agr. Sci., Vol. VIII, 
Pt. 3, pp. 312-330, June, 1917. 

Beaumont, A. B., Studies in the Reversibility of the Colloidal Condi- 
tion of Soils; Cornell Agr. Exp. Sta., Memoir 21, Apr., 1919. 



THE COLLOIDAL MATTER OF THE SOU. 135 

As may naturally be inferred the influence of the colloidal 
matter on soil conditions, especially as related to plants, is 
extremely important. This influence is exerted in a number 
of ways, modifying the physical and chemical as well as the 
biological activities within the soil. 

One important attribute imparted to soil by colloid develop- 
ment is high absorptive power. This power extends not only 
to condensation of gases, but also to water and to materials 
in solution. The water of condensation on dry soil particles 
when exposed to a saturated atmosphere is largely determined 
by the colloidal content. The absorptive capacity for mate- 
rials in solution affects both bases and acid radicals, although 
the former is usually more strongly influenced. This has a 
very important bearing on the economic use of fertilizers and 
on the loss of plant nutrients from the soil. Colloidal mate- 
rial may also function as a catalyst^ in that it may force 
certain reactions that otherwise might proceed but slowly. 

Since an adjustment is always taking place between the 
soil colloidal material and the soil solution as far as soluble 
constituents are concerned, it is readily seen that not only 
the concentration but also the composition of the latter is at 
least partially a function of the colloidal matter of the soil. 
Colloidal matter, moreover, does not exert the same absorptive 
power for all material but is capable of a certain amount of 
selection. For example, if ammonium sulfate is added to a 
soil, the ammonia is strongly taken up, which tends to release 
the sulfate ion. The continuous use of such a fertilizer on a 
soil low in active bases will ultimately result in an acid con- 
dition. This is another example of the practical importance 
of the soil colloidal matter. 

The movement of air and water in the soil is strongly in- 
fluenced by colloidal materials. In a fine soil in which the 
individual pore spaces are normally very minute the develop- 

^ A catalyst is a material capable of hastening or retarding a chemical 
reaction, the catalytic agent itself not entering into the reaction. 



136 



NATURE AND PROPERTIES OF SOILS 



ment of colloidal matter may seriously interfere with aeration 
and capillary movement of water. The loosening of a clay 
soil tends to ameliorate such conditions and to counteract 




1000 2000 5000 4000 5000 c.c. 

Fig, 23. — Curves showing the absorption of PO4 in parts per million by 
various soils from a solution of mono-calcium phosphate containing 
200 parts to the million of PO4. The volume of the percolate is 
used as the abscissas. Such absorption is a rough measure of the 
colloidal content of a soil. 

the unfavorable influence of the colloidal condition of the 
soil. Such a structural condition is largely ascribed to the 
plasticity and cohesion^ of the soil, which are in turn, of 

^ Any material which allows a change of form without rupture and 
which will retain this form when the pressure is removed, is said to be 
plastic. Putty with a proper admixture of oil is a very good example 
of a plastic body. As is well known, various materials differ in 
plasticity. 

Very closely correlated with plasticity, but not in exact similarity, is 
cohesion. By the cohesion of a soil is meant the tendency that its 
particles exhibit in sticking together and in conserving the mass intact. 



THE COLLOIDAL MATTER OF THE SOIL 137 

course, governed by the amount and the quality of colloidal 
matter present/ 

In general it is found that, other conditions being equal, 
an increase of certain types of colloidal matter increases plas- 
ticity; in other words, the ease with which a soil may be 
worked into a puddled condition becomes greater. This is a 
rather undesirable quality when too pronounced, and in clays, 
in which it is most likely to be developed because of the pres- 
ence of large amounts of mineral colloids, some means of 
decreasing the colloidal influence is advisable. This great 
plasticity is developed because the colloids, especially those 
of a gelatinous and viscous nature, facilitate the ease with 
which the particles may move over one another and yet cohere 
sufficiently to prevent disruption of the mass. In general, 
also, the greater the plasticity of a soil, the greater is the 
cohesion when dry. In soils, then, in which certain kinds of 
colloidal materials are very high, clodding may occur if the 
soil is tilled too dry because of the great tendency of the par- 
ticles to cohere. Cohesion and plasticity, as factors in soil 
structure, soil granulation, and tilth will receive further atten- 
tion later. 

It must not be inferred from the preceding discussion that 
the generation of colloidal matter is always detrimental to 
soil conditions. In sandy soils the presence of such material 
is extremely beneficial as it tends to bind the soil together, 
promotes granulation, and prevents loss of plant nutrients by 
leaching. It is only in heavy soils in which excessive amounts 
of mineral colloids may develop that a detrimental condition 
is likely to exist. This occurs because of a high cohesion and 
plasticity, because of the absorption of plant nutrients and 
because of tendencies toward acidity. The addition of organic 

^ Davis, N. B., TJie Plasticity of Clay; Trans. Amer. Cer. Soc, Vol. 
16, pp. 65-79, 1914. Cushman, A. S., TJie Colloid Theory of Plasticity; 
Trans. Amer. Cer. Soc, Vol. 6, pp. 65-78, 1904. Also, Ashley, H. E„ 
The Colloid Matter of Clay and Its Measurement ; U. S. Geol. Survey, 
Bui. 388, 1909. 



138 NATURE AND PROPERTIES OF SOILS 

matter and the development of non-plastic organic colloids 
will do much to alleviate such conditions. 

75. Resume.— The attempt to explain natural phe- 
nomena from the standpoint of crystalloidal chemistry alone 
is a failure. Nature has chosen to reveal herself, largely in 
colloidal form. Such a condition of matter is the rule and 
not the exception. Whether the sky, the ocean, or the land 
is dealt with, the larger part of the natural phenomena are 
plausibly explained only through knowledge of colloidal chem- 
istry. 

In general, the more complex the material ^nd the more 
intricate the reactions to which it is subjected, the more likely 
it is that the colloidal state will result. Proteid materials, for 
example, whether in plants or animals, are almost always col- 
loidal. It is to be expected, therefore, that the soil with its 
complicated organic and inorganic components and its rapid 
and complex reactions should generate colloidal matter and 
that material in such a state should play a prominent part 
in soil and plant activities. 



CHAPTER VII 
SOIL STRUCTURE AND ITS MODIFICATION 

The structural condition of the soil is very important to 
plant growth, since the circulation of air and water so nec- 
essary to normal development is controlled thereby. The struc- 
tural condition may be loose or compact, hard or friable, gran- 
ulated or non-granulated, as the case may be. Of these con- 
ditions granulation, especially in heavy soils, is of vital im- 
portance, since it is really a summation of all favorable struc- 
tural conditions. By granulation is meant the drawing to- 
gether of the small particles around suitable nucleii, so that 
a crumb structure is produced. The grains thus cease to 
function singly. The importance of such a structural condi- 
tion on a heavy soil is obvious. The soil becomes loose because 
of the larger units, air moves more freely, and water not only 
drains away readily wiien in excess, but responds with celerity 
to the osmotic pull of the plant. 

76. Soil structure types. — The structural condition of 
a soil can generally be attributed directly to its textural nature 
as can readily be seen by comparing sandy and clayey soils. 
For convenience of discussion two general structural groups 
may be established: (1) single-grained, and (2) compound- 
grained. In the former the particles function more or less 
separately and the soil is, as a consequence, rather open and 
friable. In the latter group the particles, being small, tend 
to stick together and the units instead of being solid are aggre- 
gates, their size and character as well as their relations to each 
other being a determining factor in the physical condition of 
the soil. As most soils are mixtures of large, medium, and 

139 



140 NATURE AND PROPERTIES OF SOILS 

small particles, it is only the coarse sandy soils on the one 
hand and very fine clayey soils on the other that ideally repre- 
sent these two groups. Most soils, especially loams, present 
combinations of the single and compound grain structures. 

Single-grain structure as found in sandy soils has certain 
obvious advantages, such as looseness, friability, good aera- 
tion, and drainage and easy tillage. On the other hand, such 
soils are often too loose and open and lack the capacity to 
absorb and hold sufficient moisture and nutrient materials. 
They are, as a consequence, likely to be droughty and lacking 
in fertility. There is only one method of improving in a prac- 
tical field way^ the structure of such a soil — the addition of 
organic matter. Organic material, if it undergoes favorable 
decomposition when incorporated with the soil, will not only 
act as a binding material for the particles but will also in- 
crease the water capacity. Nitrogen also is added and if the 
organic matter is properly supplemented with fertilizers and 
lime, the soil fertility will usually be markedly improved. A 
sandy soil high in organic matter is almost ideal from a struc- 
tural standpoint. 

The modification of the structural condition of a heavy soil 
is not such a simple problem as in the case of a sandy one. 
In the latter the plasticity and cohesion is never high even 
after the addition of large amounts of organic materials that 
rapidly develop into a colloidal state. In clays and similar 
soils the potential plasticity and cohesion ^ are always high 

* In the greenhouse or garden, structure may be modified by mixing 
different soils. This is not practicable in the field. 

* There are no satisfactory methods of determining either the plasticity 
or the cohesion of soils. For plasticity determination, see: Atterberg, 
A., Dis Plastizitdt der Ton; Internat. Mitt. f. Bodenkunde, Band I, 
Heft 1, Seite 10-43, 1911. Kinnison, C. S., A Study of the Atterberg 
Plasticity Method; Trans. Amer. Cer. Soc, Vol. 16, pp. 472-484, 1914. 

For methods of estimating cohesion : 

A good description of Schiibler's apparatus is found on page 104 of 
Bodenkunde, by E. A. Mitscherlich, published by Paul Parey, Berlin, 
in 1905. Haberlandt, H., Uber die Kohdreszenz, Verhalinisse ver- 
schiedener Bodenarten ; Forsch. a. d. Gebeite d. Agri.-Physik., Band I, 
Seite 148-157, 1878. Also, Wissenschaftlich praTctische Untersuchungen 



SOIL STRUCTURE AND ITS MODIFICATION 141 

due to the presence of large amounts of complex hydrated 
aluminum silicates in a colloidal condition. The more plastic 
a soil becomes, the more likely it is to puddle/ especially if 
worked when wet. Moreover, a soil of high plasticity is prone 
to become hard and cloddy when dry, due to the cohesive ten- 
dencies of the small particles. Heavy soils must, therefore, 
be treated very carefully, especially in tillage operations. If 
plowed too wet, puddling occurs, the aggregation of particles 
is broken down, and an unfavorable structure is sure to re- 
sult. If plowed too dry, great lumps are turned up which 
are difficult to work down into a good seed-bed. In a sandy 
soil, no such difficulties are encountered.^ 

Granulation or the production of a compound-grain struc- 
ture is the only means of correcting the physical condition of 
a heavy fine-grained soil. In this process the small particles 
are drawn towards innumerable suitable nucleii and a porous 
structure is developed. The size of the individual pore spaces 
is thereby increased and air and water drainage is facilitated. 
The structural condition in reality simulates a single-grain 
state with this important difference, however: the particles 
are porous and not solid. Unless a hea\'y soil possesses at least 
some granulation, it is more or less unfit for agricultural 
operations. (See Fig. 24.) 

77. Granulation. — While it is possible to list the factors 

auf dem Gebeite des Pflanzenbaues ; Band I, Seite 22, 1875. Puchner, 
H., Untersuchungen iiber die Kohareszenz der Bodenarten; Forsch. a. d. 
Gebiete d. Agri.-Physik., Band 12, Seite 195-241, 1889. Atterberg, A., 
Die Konsistenz und die Bindigkeit der Boden; Internat. Mitt. f. Boden- 
kunde, Band II, Heft 2-3, Seite 149-189, 1912. Cameron, F. K., and 
Gallagher, F. E., Moisture Content and Plvysical Condition of Soils; 
V. S. Dept. Agr., Bur. Soils, Bui. 50, 1908. 

*Wlien a soil in a plastic condition has been kneaded until its pore 
space is much reduced and it has become practically impervious to air 
and water, it is said to be puddled. The development of gelatinous 
and viscous colloidal materials seems to be the controlling factor in 
such a condition, the pore space of a puddled soil being largely filled 
with such material. When a soil in this condition dries, it becomes hard 
and dense. 

* Sandy soils are often plowed rather wet in order to render them 
more compact than they normally would be. 



142 



NATURE AND PROPERTIES OF SOILS 



that bring about granulation in a soil, it is difficult to state 
specifically just why this phenomenon takes place. It has been 
suggested that much of the granule formation in the soil is 
due to the contraction of the moisture around the particles 
when, for any reason, the moisture content is reduced. It 
is known that the soil particles tend to be drawn together 
by this reduction in the soil-moisture, due to the pulling power 
of the thinned films. 

If to this condition is added a material which tends to exert 
not only a drawing power on loss of moisture, but also a bind- 




FiG. 24.— A well granulated soil and a puddled soil. Organic matter 
plays an important role in structural condition. 

ing and cementing power when dry, all the essentials for suc- 
cessful granulation are present. This second force is found 
in. the colloidal material existing in considerable quantities in 
heavy soils. Such materials have already been shown to deter- 
mine the cohesion of the soil. The influence of the colloidal 
material is considered by many authorities as the more im- 
portant in the structural adjustments of the soil. 

It is evident that if cohesion and plasticity are to function 
in granulation — or, in other words, locally in the soil instead 
of generally and uniformly as when clodding or puddling 
occurs — a certain moisture content must be maintained. In 
a soil subject to such a condition, the cohesive forces being 



SOIL STRUCTURE AND ITS MODIFICATION 143 

localized, the internal strains and pressures are unequal and 
a tendency arises for the mass to divide along lines of weak- 
ness into groups of particles. The binding capacity of col- 
loidal material, as well as of salts deposited from the soil 
solution, tends to make such a crumb structure more or less 
permanent. The moisture content most favorable for granu- 
lation seems to be that which is optimum for plant growth.^ 

78. — Forces facilitating granulation.- — Granulation is 
nothing more or less than a favorable condition brought 
about by the force exerted by a variable water film and the 
pulling and binding capacities of colloidal material, operating 
at numberless localized foci. It is evident that any influence 
or change in the soil which will cause a greater localization 
of these operative forces will promote the aggregation of the 
particles. The addition of materials from extraneous sources 
is also a practice that may tend to develop lines of weakness 
and thus cause a more intense activity of the forces at work. 

The conditions, additions, and practices tending to develop 
or facilitate a granular structure in soils may be listed under 
six heads: (1) wetting and drying of the soil, (2) freezing 
and thrawing, (3) addition of organic matter, (4) action of 
roots and animals, (5) addition of lime and (6) tillage. Only 
the last two need additional consideration. 

79. Granulating influence of lime.^ — One of the effects 
of lime in the soil, especially of the oxide and hydroxide forms, 

^ Cameron, F. K., and Gallagher, F. E., Moisture Content and Physical 
Condition of Soils; U. S. Dept. Agr., Bur. Soils, Bui. 50, p. 8, 1908. 

^ Fippin, E. O., Some Causes of Soil Granulation; Trans. Amer. Soc. 
Agron., Vol. 2, pp. 106-121, 1910. Czermak, W., Bin Beitrag zur Erkent- 
uis der Verdnderungen der Sog physilcalischen Bodeneigensliaften durch 
Frost, Eitse, und die Beigabe einiger SaJze; Landw. Ver. Stat., Band 
76, Heft 1-2, Seite 73-116, 1912. Also, Ehrenberg, P., und Eomberg, 
G. F. von, Zur Frostwirbung auf den Erdboden; Jour. f. Landw. 
Band 61, Heft 1, Seite 73-86, 1913. 

'Lime in a strictly chemical sense refers only to calcium oxide (CaCf). 
The term is used here with an agricultural meaning, including all cal- 
cium and magnesium compounds which are ordinarily added to the soil 
to correct acidity, thus including not only calcium oxide but calcium 
hydroxide and calcium carbonate [Ca(OH)o and CaCOa] as well. 



144 NATURE AND PROPERTIES OF SOILS 

is a flocculating action. This agglomeration, as already ex- 
plained, is the drawing together of the finer particles of a 
soil mass into granules. When calcium hydroxide is mixed 
with water containing fine particles in suspension there is 
almost immediately a change in the arrangement of the par- 
ticles. They first draw together in light, fluffy groups, or floc- 
cules, which then rapidly settle so that the supernatant 
liquid is left clear or nearly so. This phenomenon is termed 
flocculation, because of the peculiar appearance of the 
aggregates. This flocculating tendency when lime is added 
goes on in the soil as well as with suspensions, although more 
slowly. In general, the lime tends to satisfy the absorptive 
capacity of the colloidal material and by throwing down these 
colloids develops lines of weakness. The cohesive power of 
the soil is thus localized and agglomeration must necessarily 
occur. The various forms of lime differ in their flocculating 
capacities, calcium oxide and hydroxide being very active, 
while calcium carbonate is relatively inactive in this regard. 

It must not be inferred that lime is generally added for its 
flocculating influence. It is used primarily for other reasons, 
the amounts applied being in general too small to have very 
much influence on the structural condition of the soil. War- 
ington,^ however, reports a statement of an English farmer 
to the effect that by the use of large quantities of lime on 
heavy clay soil, he was enabled to plow with two horses instead 
of three. It is generally true that soils rich in lime are well 
granulated, and maintain a much better physical condition 
than soils of the same texture that are low in lime. 

80. Tillage.- — Tillage aims to accomplish three primary 

^ Warington, E., Physical Properties of Soils, p. 33, Oxford, 1900. 

' For a very complete review of the theory and practice of plowing 
and cultivation, with a complete bibliography: Sewell, M. C, Tillage: 
A Bevieto of the Literature; Jour. Amer. Soc. Agron., Vol. II, No. 7, 
pp. 269-290, Oct., 1919. 

The following books upon the mechanics of tillage may prove helpful: 

Davidson, J. B., and Chase, L. W., Farm Machinery and Farm Motors; 
New York, 1908. 

The Oliver Ploiv Boole; South Bend, Ind., 1920. 



SOIL STRUCTURE AND ITS MODIFICATION 145 

purposes: (1) modification of the structure of the soil; (2) 
disposal of rubbish or other coarse material on the surface, and 
the incorporation of manures and fertilizers into the soil ; and 
(3) the deposition of seeds and plants in the soil in position for 
growth. 

The most prominent of these purposes is the modification 
of the soil structure. This affects the retention and movement 
of moisture and air, the absorption and retention of heat, 
and either promotes or retards the growth of organisms. The 
creation of a soil-mulch is merely a change in the structure 
of the soil at such times and in such a manner as may prevent 
the evaporation of moisture. In fine-textured soils, in which 




1 Z 5 

Fig. 25. — Three types of plow bottoms; 1, stubble; 2, sod; 3, general 

purpose. 

the granular structure is most desired, tillage may have an 
important influence on the formation or destruction of gran- 
ules. As has been pointed out, any treatment that increases 
the number of lines of weakness in the soil structure facili- 
tates the activities of the moisture films and the colloidal mate- 
rials in producing soil granules. Tillage shatters the soil and 
breaks it into many small aggregates, which may be drawn 
together and loosely cemented as a result of the evaporation 
of moisture. The more numerous the lines of weakness pro- 
duced, the more pronounced is the granulation; and, con- 
versely, the fewer the lines of weakness produced, the more 
coarse and cloddy is the structure. 

According to their mode of action, tillage implements may 

Kamsower, H. C, Equipment for the Farm and Farmstead; Boston, 
1917. 
King, F. H., Physics of Agriculture; Chap. XI, Madison, Wis., 1910. 



146 NATURE AND PROPERTIES OF SOILS 

be grouped as follows: plows, cultivators, packers and 
crushers, 

81. The action of the plow. — The moldboard plow 
brings about its effects because of the differential stresses set 
up in the furrow slice as it passes over the share and the 
moldboard. The soil in immediate contact with the plow sur- 
face is retarded by friction, and the layers above tend to 
slide over one another much as the leaves of a book when they 
are bent. If the soil is in just the proper condition, maximum 
granulation results ; but if the moisture is too high or too low, 
puddling or clodding may follow, especially on a heavy soil. 

Not only does a shearing occur, but this shearing is differ- 
ential, due to the slope of the share and especially to the curve 
of the moldboard. When the soil is to be turned over with 
the least expenditure of energy, the share is sloping and is 
set to deliver a slanting cut, and the moldboard is long and 
gently inclined. This allows the furrow slice to be turned with 
little granulation and with a minimum effort. When maxi- 
mum granulation and pulverization are desired, the mold- 
board is short and sharply turned, and the share is less slop- 
ing and the cutting edge less slanting. Such conditions make 
for the development of more friction and the generation of 
those internal twisting and shearing stresses necessary for 
good granulation. The sharper the bending of the furrow 
slice, the greater are the internal stresses set up. Various 
types of moldboards and shares designated for special soils 
and particular operations are on the market. (See Fig. 25.) 

The disc plow is a sharp rolling disc set at such an angle 
that it slices off and turns over the soil, pulverizing it fairly 
effectively somewhat after the manner of the moldboard plow. 
One advantage of the disc plow is its lighter draft, due to 
a rolling rather than a sliding friction in the soil. In prac- 
tice it is especially effective on very dry, hard soil. 

While the plow is the very best pulverizing agent when 
optimum soil-moisture conditions prevail, it is also a most 



SOIL STRUCTURE AND ITS MODIFICATION 147 

effective puddling agent when the soil is wet. Therefore, care 
in the judging of optimum conditions for plowing is a most 
important feature in the maintenance and encouragement 
of soil granulation. A careful study of the moisture con- 
ditions in a clay soil is especially necessaiy in order to de- 
termine just what is the correct moisture content for good 
plowing. That this condition must be gauged carefully and 
immediate use made of the advantages it offers is shown by 
its narrow limits. A few days may suffice for the moisture to 
pass through and beyond such a condition. A clay soil is so 




Fig. 26. — A six-shovel cultivator. 



difficult to handle at best that no opportunities such as are 
offered by optimum moisture conditions should be lost. More- 
over, a heavy soil plowed too dry or too wet does not regain 
its normal granular condition for several seasons. Such care 
is unnecessary with a sandy soil. 

82. Cultivators, packers and crushers. — The many 
types of cultivators may be grouped under three heads: (1) 
cultivators proper, (2) levelers and harrows, and (3) seeder 
cultivators. The action of all these implements is the same 
in that they stir the soil, at the same time loosening the struc- 
ture and cutting off weeds. AVhile the action is much shal- 
lower than with the plow, the same attention should be paid 
to moisture conditions. Particularly is this true in pulveriza- 



148 NATUKE AND PROPERTIES OF SOILS 

tion immediately after plowing. When the moisture condi- 
tions are optimum, the clods are more easily shattered and 
the formation of a suitable seed-bed is speedily accomplished. 

The cultivators proper are well represented by the ordinary 
corn cultivator whether equipped with shovels, knives or discs. 
Under the leveler and harrow type may be placed the spike 
and spring-tooth harrow, the various kinds of weeders, the 
acme harrow and the disc harrow. The latter may be equip- 
ped with solid, cut-away, or spading discs. The grain drill, 
either of the press or disc type, is a representative of the 
seeder cultivators, which considerably influence the structural 
condition of the soil although such action is not their primary 
purpose, (See Fig. 26.) 

Packing and crushing are ordinarily performed by the same 
implement, since any tool that compacts does a certain amount 
of crushing; and, conversely, any implement that crushes the 
soil does some compacting. Such an implement as the culti- 
packer cultivates, packs and promotes granulation in one 
operation. The difficulty of establishing a rigid classification 
is evident. 

Rollers may be of the solid or barrel type, the corrugated 
type, or the bar type. The subsurface packer is also included 
in this group. Rollers tend to force the soil particles nearer 
together and smooth the surface. If at the same time they 
establish a soil-mulch so much the better. The rolling of the 
land after seeding is an attempt to stimulate the capillary 
movement of the water and to hasten germination by bring- 
ing the seed in closer contact with the soil. 

The planker, drag, or float is a common type of single 
crusher. It is generally broad and heavy, without teeth and 
is dragged over the soil. The lumps are rolled under its edges 
and ground together in such a manner as effectively to reduce 
their size. The soil is leveled and smoothed at the same time. 
This implement may be used instead of a roller in many cases. 
(See Fig. 27.) 



SOIL STRUCTURE AND ITS MODIFICATION 149 

83. Soil tilth. — The previous data and discussion have 
clearly shown the very great importance of structure in the 
successful handling of the soil in the field. Since good phy- 
sical condition will reflect itself on crop yield it is evident 
that structure must ultimately be considered in .relation to 
all plant growth. This relationship is usually expressed by 
the term tilth. While structure refers to the arrangement of 
the particles in general, and granulation to a particular aggre- 
gate condition, tilth goes one step farther and includes the 
plant. Tilth, then, refers to the physical condition of the soil 




Fig. 27. — A planker or drag, useful in the crushing of clods. 

as related to crop growth. It may be poor, medium, good, or 
excellent, according to circumstances. Good tilth may de- 
mand in many soils maximum granulation, in others only a 
medium development. Tillage operations by influencing the 
structure of the soil aim to develop optimum tilth. Optimum 
tilth always implies the presence of water since the best phys- 
ical relationships cannot be developed without such moisture 
conditions. 

84. Summary. — The factors which control the struc- 
tural condition of the soil to the greatest extent are plasticity 
and cohesion, their influence intensity being due directly to 
the presence of certain kinds of materials, especially hydrated 
aluminum silicates, in a colloidal state. As plasticity and 
cohesion increase the tendencies of a soil to puddle when wet 



150 NATURE AND PROPERTIES OF SOILS 

and to clod when dry are augmented. Therefore in heavy 
soils a modification in these factors is advisable, through a 
careful control of moisture and a bettering of the granular 
structure of the soil. Grranulation, while due to some extent 
to the influence of the water film, is traceable largely to col- 
loidal matter both mineral and organic. It is really a con- 
centration of the forces of cohesion and plasticity around num- 
berless localized foci. Granulation takes place under the in- 
fluence of wetting and drying, freezing, plants and animals, 
addition of lime and organic matter, and tillage operations, 
especially plowing. The farmer exerts a modifying influence 
on structure most efficiently by increasing the organic content 
of the soil and by plowing. He is, of course, aided and abetted 
by natural forces. 

Efficient tillage requires good judgment in the selection of 
proper implements and mechanical skill in their operation. 
It demands besides an understanding of the properties of soils 
and a knowledge of their plant relationships. Sandy soils are 
easily handled provided sufficient organic matter is main- 
tained. Such cannot be said of clayey soils. Due to the high 
cohesion and plasticity of heavy soils the moisture zone for 
successful tillage is particularly narrow. The ability to detect 
when this zone has been reached in a clay soil is one of the 
essentials of its successful management. Another essential 
is the effective widening of such a zone by granulation oper- 
ations. 

The optimum moisture condition for tillage is generally near 
the optimum condition for plant growth — a happy coinci- 
dence, since by regulating the moisture content for plant devel- 
opment conditions are rendered most favorable for all soil ac- 
tivities. It is thus possible to produce in one operation that 
desideratum in all soil physical operations, an optimum tilth. 



CHAPTER VIII 

TEE FORMS OF SOIL-WATER AND THEIR 
CHARACTERISTICS ' 

A SOIL, in order to function as a medium for plant growth, 
must contain a certain amount of water. This moisture pro- 
motes the innumerable chemical and biological activities of the 
soil, it acts as a solvent and carrier of nutrients, and in addi- 
tion it functions as a nutrient itself. The amount, character, 
and control of the soil-moisture must evidently be reckoned 
with in any study of soil and plant relationships, whether they 
are of a practical or a theoretical nature. The productivity 
of a soil is often a direct function of its moisture condition. 

85. Forms of soil-water. — As has already been demon- 
strated, a soil of a given volume weight has a definite pore 
space which may be occupied largely by air or by water, or 
shared by both, as the case may be. Of course, an ideal soil 
for growth is one in which there is both air and water, the 
proportions depending on the texture and the structure of 
the soil and the character of the crop. Assuming for the time 
being, however, that the pore space is almost entirely filled 
with w^ater, or, in other words, that the soil is saturated, three 
forms of w^ater are found to be present — hygroscopic, capillary 
and gravitational. These forms differ not only in the amount 
and proportion of the solutes which they carry but also in the 
positions that they occupy in their relation to the larger soil 
particles and the accompanying colloidal complexes. 

^ Keen, B. A., Belations Existing Between the Soil and Its Water 
Content; Jour. Agr. Sci., Vol. X, Part 1, pp. 44-71, Jan., 1920. A 
good review of the subject. 

151 



152 NATURE AND PROPERTIES OF SOILS 

If an absolutely dry soil is exposed to a moist atmosphere, 
it will absorb moisture rather rapidly until the colloidal sur- 
faces are in equilibrium with the air as far as water vapor is 
concerned. Other conditions being equal, maximum water 
will be taken up from an atmosphere which is saturated with 
moisture. The moisture thus taken up is called hygroscopic 
water, its amount being determined quite largely by the mag- 
nitude of the colloidal material present in the soil. 

On adding more water, it will be found that the absorptive 
power of the soil has been by no means satisfied by the hygro- 
scopic water. Moisture will still be taken up by the colloidal 
complexes and it will also collect in the interstices between 
the soil particles. This water which is above and beyond the 
hygroscopic is generally called the capillary. That part held 
by the colloidal complexes is very similar in characteristics to 
the hygroscopic water in that it is tightly held and is more 
or less immovable. That portion in the interstices, especially 
the larger spaces, is in the form of a film, is loosely held, and 
responds to capillary action. While typical capillary water 
is much different from hygroscopic moisture, it grades into 
the latter with no sharp line of demarcation. 

Once the capillary capacity of the soil is satisfied, a third 
form of water may appear. This water is but slightly in- 
fluenced either by the colloidal complexes or the larger soil 
particles and consequently is free to respond to the pull of 
gravity. It is called the free or gravitational moisture and 
is the water which passes through the soil and appears in 
streams and rivers bearing in solution the tremendous amounts 
of soluble salts which are every year lost from the land. 

86. Hygroscopic water. — The hygroscopic water in a 
soil has been spoken of as the water of condensation, or ab- 
sorption. It is, however, quite distinct from water condensed 
on a surface colder than the moist atmosphere in which it is 
placed. All bodies possess the power, to a greater or less de- 
gree, of absorbing water even when at the same temperature 



THE FORMS OF SOIL-WATER 153 

as the air with which they are in contact, provided, of course, 
that the air contains water-vapor. Such condensation is 
largely a function of the surface exposed. 

One of the characteristics peculiar to colloidal materials is 
a high absorptive power for water, whether it is presented in 
the form of a liquid or vapor. This capacity is due to the 
tremendous surface exposed by matter in a colloidal state, 
which not only may hold the moisture physically but may 
even force it into loose chemical combination.^ The hygro- 
scopic water is probably not in the form of a film around 
the particles but in a much more intimate relationship. That 
which is held physically is probably, in part at least, in a con- 
dition of solid solution. If any of the hygroscopic water'Ms 
held chemically, the bond is probably a rather loose one. 

A large proportion of the hygroscopic moisture is obviously 
not in a liquid state and consequently is immovable as such. 
When a hygroscopically saturated soil is exposed to a partially 
saturated air, a portion of the hygroscopic moisture will be 
lost through vaporization. In order to expel the remainder 
of the hygroscopic water, the soil must be heated. For con- 
venience of determination, it is generally assumed that all of 
the hygroscopic moisture will be driven from an air-dry soil 
by heating it for four or five hours at a temperature of 100° 
or 110° C. This is only an assumption, however, as some of 
the moisture in intimate relationship with the colloidal com- 
plexes probably still remains. 

The amount of energy necessary to expel the hygroscopic 
moisture from the soil is very great, since its only movement 
is thermal and because it is held so closely. As so much 
energy is expended in removing this water, it is reasonable to 

*See, Bouyoucos, G. J., Classification and Measurement of the Dif- 
ferent Forms of Water in the Soil by Means of the Dilatometer Metlwd; 
Mich. Agr. Exp. Sta., Tech. Bui. 36, Sept., 1917. Eelationship between 
the Unfree Water and the Heat of Wetting of Soils and its Significance ; 
Mich. Agr. Exp. Sta., Tech. Bui. 42, Mar., 1918. A New Classification 
of the Soil Moisture; Soil Sei., Vol. XI, No. 1, pp. 33-47, Jan., 1921. 



154 NATURE AND PROPERTIES OF SOILS 

expect that a certain amount of heat of condensation will be 
apparent when it is resumed.^ Patten ^ and Bouyoucos ^ offer 
the following quantitative data concerning this point : 

Table XXVIII 

HEAT EVOLVED BY WETTING SOILS DRIED AT 110° C. 



Soil 



Calories to a 
Kilo of Dry Soil 



Quartz sand 

Norfolk sand 

Hagerstown loam 

Miami silt loam 

Cecil clay 

Superior clay 

Muck (25% organic matter) 
Peat 



000 
347 
1108 
1742 
3376 
5158 
6413 
22185 



87. Determination of the hygroscopic coefficient. — 

The methods for the determination of the maximum liygro- 
scopicity of a soil, or, in other words, the hygroscopic coeffi- 
cient, are simple in outline. The soil, in a thin layer, is ex- 
posed to an atmosphere of definite humidity under conditions 
of constant temperature and pressure. Complications arise 
from the necessity of using a very thin layer of soil, from the 
difficulty of controlling humidity, and from the tendency of 
capillary water to form in the soil interstices before the hygro- 
scopic capacity is satisfied. The question of how long the 
exposure should take place has not been definitely settled. It 

^ The tremendous heat of wetting is probably due to the latent heat 
of water, to the attraction that soils have for water and to the condition 
into which the water is transformed. The heat of condensation is so 
large as to suggest the probability of a change in the aggregation of 
the moisture thus absorbed. 

^Patten, H. E., Heat Transference in Soils; U. S. Dept. Agr., Bur. 
Soils, Bui. 59, p. 34, 1909. 

' Bouyoucos, G. J., BelationsMp betu-een the Vnfree Water and the 
Beat of Wetting of Soils and its Significance; Mich. Agr. Exp. Sta., 
Tech. Bui. 42, Mar. 1918. 



THE FORMS OF SOIL-WATER 155 

is evident, therefore, that not only must any method be more 
or less arbitrary but that its value can only be comparative. 

In the actual procedure/ the sample of soil may be air- 
dried or dried at 100° or 110° C. If the former method is 
followed, the sample after exposure is heated for four or five 
hours at 100° or 110° C, the loss being considered as hygro- 
scopic water. If oven-dried soil is utilized, the gain in weight 
due to the exposure to the moist air is the hygroscopic mois- 
ture. If a saturated air is made use of, the gain is maximum 
hygroscopicity, from which can be calculated the percentage 
of hygroscopic water based on dry soil, called the hygroscopic 
coefficient. If a partially saturated air is utilized, a sample 
of stock soil, the hygroscopic coefficient of which is known, is 
exposed at the same time. The determination on the known 
sample shows what proportion of possible hygroscopic water 
has been taken up. From this the hygroscopic coefficient of 
the unknown soil sample can be calculated.- 

88. Hy^oscopic capacity of soils. — Since hygroscopic- 
ity depends almost directly on the colloidal nature of the soil, 
it is evident that texture, external factors being under con- 
trol, will be an important factor in determining the hygro- 
scopic coefficient. When the organic matter of soils is more 
or less the same in amount, the inorganic colloids seem to con- 

"■ Hilgard, E. W., Soils; pp. 196-201, New York, 1911. This method 
ia practically the same as that used for the comparative estimation of 
the colloidal content of the soil^ the hygroscopic coefficient being the 
comparative figure obtained. See note to paragraph 74 of this text. 

Bouyoucos determines the hygroscopic coefficient in an approximate 
way by means of the dilatometer method. The dilatometer is an 
apparatus which measures the expansion of water on freezing. If a given 
amount of soil and water is reduced below zero, the expansion attained 
will reveal the amount of water remaining unfrozen, due to its soil 
relationships. Bouyoucos finds that the amount of moisture unfrozen 
after supercooling to —4° C. (slightly more freezes at -78° C.) correlates 
fairly well with the hygroscopic coefficient. Bouyoucos, G. J., A New 
Classification of Soil Moisture; Soil Sci., Vol. XI, No. 1, pp. 33-47, 
Jan., 1921. 

^Alway, F. J., and Clarke^ V. L., Use of Two Indirect Methods for 
the Determination of the Hiigroscopic Coefficients of Soils; Jour. Agr. 
Kes., Vol. VII, No. 8, pp. 345-351, Nov., 1916. 



156 



NATURE AND PROPERTIES OF SOILS 



trol the hygroscopicity. The following; figures from Briggs 
and Schantz/ by whom the hygroscopic coefficient was deter- 
mined by exposing air-dry soil at 20° C. to a saturated atmo- 
sphere and then drying at 110° C, illustrate this point. The 
organic matter was not a serious disturbing factor. 

Table XXIX 

HYGROSCOPIC CAPACITY OF VARIOUS SOILS EXPRESSED IN PER- 
CENTAGE BASED ON DRY SOIL'^ 



Soils 



Coarse sand .... 

Fine sand 

Sandy loam . . . . 
Fine sandy loam 

Loam 

Clay loam 

Clay 



Percentage 


Hygroscopic 


OF Clay 


Coefficient 


1.6 


.5 


3.9 


1.5 


7.5 


3.5 


12.9 


6.6 


14.4 


9.6 


22.0 


11.4 


32.5 


13.2 



' Briggs, L. J., and Schantz, H. L., The Wilting Coefficient for IHf- 
ferent Plants and Its Indirect Determination ; U. S. Dept. Agr., Bur. 
Plant Ind., Bui. 230, p. 65, Feb., 1912. See also, Loughridge, R. H., 
Investigations in Soils Physics; Calif. Agr. Exp. Sta., Rep. of Work of 
the Agr. Exp. Stations of Calif, for 1892-3-4, pp. 76-77. Ammon, Georg., 
Vntersuchungen iiber das Condeiisationsvermogen der Bodenconstituenten 
fur Gase; Forseh. a. d. Gebiete d. Agri.-Physik., Band II, Seite 1-46, 1879. 
Dobeneek, A. F., von, Untersuchungen iiber das Ahsorptionsvermogen 
und die Hygroskopizitdt der BodenTconstituenten ; Forseh. a. d. Gebiete 
d. Agri.-Physik., Band XV, Seite 163-228, 1892. 

* During the many years of soil investigation, especially where the 
problems had to deal either directly or indirectly with moisture, five 
methods of water expression have been evolved, their use depending on 
the nature of the work and on the points to be expressed. They may be 
listed under two general heads: 

A. Percentage expression 

1. Percentage on a dry basis 

2. Percentage on a wet basis 

B. Volume expression 

1. Cubic inches to the cubic foot of soil 

2. Percentage by volume 

3. Surface inches 

A soil carrying 25 per cent, of water on the dry soil basis contains 20 
per cent, on the moist basis (soil plus water). The former method is 



THE FORMS OF SOIL-WATER 



157 



Apparently, the finer the soil, the higher the hygroscopic 
coefficient. This is due to the fact that most of the inorganic 
colloidal matter is carried by the finer separates. In consid- 
ering the hygroscopicity, however, the influence of the organic 
matter must not be forgotten. Organic colloidal matter has 
a veiy marked influence on absorption, and as the organic 
matter of the soil increases, the hygroscopicity rises rapidly. 
The following data from Beaumont^ is interesting in this 
respect : 

Table XXX 

THE HYGROSCOPIC COEFFICIENT^ COMPARED TO CERTAIN OTHER 

SOIL FACTORS 



Soil 


Clay 

% 


Igni- 
tion 

% 


Humus 

% 


Hygro- 
scopic 

Coeffi- 
cient 

% 


Dunkirk silty clay loam, surface 
Dunkirk silty clay loam, subsoil 

Clyde clay loam, surface 

Vergennes clay, subsoil 


12.9 
20.0 

20.1 
74.5 


5.08 
3.05 

14.54 
5.79 


1.26 
.20 

4.34 
.49 


3.80 

5.77 

18.90 
17.40 



In comparing the two Dunkirk soils it is apparent that the 
colloidal clay is the dominant factor in determining the mag- 
preferable in that the basis for calculation is not a changeable one as is 
the weight of moist soil. The dry basis is practically always used in 
soil work. 

Where two soils of different volume weight are compared, the per- 
centage relationship does not give a true idea of the relative amounts 
of water present. A volume expression should then be used. If a cubic 
foot of soil, weighing 100 pounds, contains 10 pounds of water it would 
be carrying (10 X 27.6) or 276 cubic inches of water. This would 
equal (276-^1728) X 100 or 15.9 per cent, by volume or (10->-.5.2) = 
1.92 surface inches. 

^ Beaumont, A. B., Studies iii the Eeversibility of the Colloidal Condi- 
tion of Soils; Cornell Agr. Exp. Sta., Memoir 21, pp. 501-504, April, 
1919. 

* Moisture content in this text unless otherwise indicated will always 
be expressed on the dry soil basis. 



158 NATURE AND PROPERTIES OF SOILS 

nitude of the hygroscopic coefficient. With the Clyde and 
Vergennes, however, the organic colloidal matter is dominant, 
since the Clyde with only 20 per cent, of clay has a higher 
hygroscopic figure than the Vergennes which carries 74.5 per 
cent, of that separate. The Clyde clay loam and the Dunkirk 
subsoil have the same amount of clay, yet the former pos- 
sesses a hygroscopic coefficient over three times larger. 

Two external conditions seem to be important in determin- 
ing the amount of hygroscopic water in soils — (1) humidity 
and (2) temperature. It has been definitely established that 
the higher the humidity the higher the content of hygro- 
scopic moisture. An air-dry soil will, therefore, contain less 
moisture in a dry atmosphere than in one carrying large 
amounts of water-vapor. When the soil is in contact with a 
saturated air it will take up hygroscopic water to its full 
capacity and be at the point spoken of as the hygroscopic 
coefficient. As the soil air is generally considered to be satu- 
rated or almost saturated with water- vapor, ^ except in the 
surface layers or during periods of protracted drought, a soil 
in normal condition may be considered, for all practical pur- 
poses, to be at its maximum hygroscopicity. An increase of 
the temperature of the saturated atmosphere seems to increase 
hygroscopicity. With a partially saturated air the influence 
seems to be in the opposite direction.^ This, however, is not 
an important practical point. 

The hygroscopic coefficient, defined as the maximum hygro- 
scopic water that a soil will hold, is controlled largely by the 
texture and organic content of the soil. It may vary from a 
very low figure in a sandy soil to as high as 15 per cent, for 
a clay high in organic matter. With a muck or peat, the per- 

^ Eussell, E. J., and Applyard, A., The Atmosphere of the Soil: Its 
Composition and Causes of Variation; Jour. Agr. Sei., Vol. VII, Part 1, 
p. 5, 1915. 

^ For a full discussion of this point, see Lipman, C. B., and Sharj), 
Li. T., a Contribution to the Subject of the Hygroscopic Moisture of 
Soils; Jour. Phys. Chem., Vol. 15, No. 8, pp. 709-722, Nov., 1911. 



THE FORMS OF SOIL-WATER 159 

centage would be considerably higher, in some cases reaching 
50 or 60 per cent. It must always be kept in mind, however, 
that the point designated as the hygroscopic coefficient is more 
or less arbitrary and that there is no sharp line of demarca- 
tion between the moisture designated as hygroscopic and that 
which lies near it, but is called capillary, 

89. The capillary water.^ — The moisture above the 
hygroscopic coefficient but not free to respond to gravity is 
generally spoken of as the capillary water. The portion of 
this moisture lying in contact or in the immediate neighbor- 
hood of the hygroscopic water is probably capable of only 
sluggish diffusion movement if any.^ This part of the capillary 
moisture is held largely by the colloidal matter and may be 
considered as transitional between the true hygroscopic and 
the more active capillary portion. Although so closely related 
to the hygroscopic water in general properties and character- 
istics, the soil does not assume it by absorption from vapor- 
laden air. This separates it at least analytically from the 
hygroscopic form of moisture. Moreover, it is probably 
largely in the liquid state, which is hardly true of all of the 
hygroscopic water. 

The more active capillary water exists in the large inter- 
stices and as a film over the particles and the colloidal com- 
plexes. It is held rather loosely by the soil, yet strongly 
enough to counteract gravitation. This part of the capillary 
moisture, being more or less beyond colloidal influence, is 
free to respond to the forces active in true solutions and, there- 
fore, may move from place to place as equilibrium stresses 
may demand. While the inner portion of the capillary water 
is held by the absorptive power of the colloidal surfaces, the 
outer and freer portion is maintained by the surface tension 

^ The colloidal conceptions regarding soil-moisture has made it advis- 
able to give the term capillary a broader significance than its root 
meaning justifies. 

^Bouyoucos, G. J., A Neiv Classification of the Soil Moisture; Soil 
Sci., Vol. XI, No. 1, pp. 33-47, Jan., 1921. 



160 NATURE AND PROPERTIES OF SOILS 

of the water film. The distinctive characteristics of these two 
portions of the capillary water are due to their controls — 
colloidal in one case, surface tensional in the other.^ 

While the outer portion of the capillary water is undoubt- 
edly in the form of a more or less continuous film from par- 
ticle to particle, the bulk of such moisture probably exists 
normally in the interstices between the soil grains. Such a 
condition arises because of the pressure developed by the 
force of surface tension. The pressure due to surface tension, 
however it may be expressed, varies with the curvature of 
the film and is proportional to twice the surface tension di- 
vided by the radius. The less the radius the greater the cur- 
vature and, therefore, the greater the stress developed by sur- 
face tension.^ 

The situation so far as the soil is concerned may be ex- 
plained in an empirical way as follows : Suppose that two par- 
ticles, each carrying a capillary water film, be brought into 
such contact that the films coalesce. There are now two 
distinct surfaces, that at A, A' (see Fig. 28), with the curva- 

* Bouyoucos classifies these two types of capillary water as free (the 
more active) and capillary-absorbed (the inner group). The distinction 
is made on the basis of his dilatometer results, the portion which freezes 
at about 0°C being considered as the more active or free. 

Bouyoucos, G. J., A New Classification of the Soil Moisture; Soil 
Sci., Vol. XI, No. 1, pp. 33-47, Jan., 1921. 

^Surface tension is the tension of a liquid surface by virtue of which 
it acts like an elastic enveloping membrane, tending always to contract 
to the minimum area. While molecules in the interior portion of the 
liquid are attracted in all directions and are thus at equilibrium, those 
on the surface are attracted by an overbalancing force toward the 
interior. In measurement, surface tension is considered as the force with 
which the surface on one side of a line, one centimeter long, pulls against 
that on the other side of the line. It is generally expressed in dynes. 
The pressure due to surface tension varies with the curvature of the film. 
It is usually expressed as: ' 

p^2T 

r 
where P is the pressure; T, surface tension; and r, the radius of the 
drop. As the radius becomes less, the curvature increases and the pres- 
sure due to surface tension increases. An increase of T will increase 
the pressure, P. 



THE FORMS OF SOIL- WATER 



161 



ture of the original film, and that at B, which is very acute 
and which naturally must exert a very great outward pull. 
Under the stress of this pull developed by the surface tension 
acting in this film of very great curvature, the water is drawn 
into the space between the particles, where it becomes thicker 
than the capillary film about the particles. The readjustment 
continues until the forces developed by the two films become 
equal. An equilibrium is now established. In the soil the 
tendency towards adjustment is somewhat similar in so far 




Fig, 28. — A conventional diagram showing the coalescence and read- 
justment of the outer capillary water film of two particles when 
brought in contact. At the left is shown the condition before the 
adjustment with a sharp angle at B; on the right, the films are at 
equilibrium with a thickening at B due to movement from A and A'. 



as the outer capillary water is concerned. Complete equilib- 
rium is probably never reached, however, due to constantly 
disturbing factors. 

90. The determination of the amount of capillary 
water in the soil. — The capillary water in a sample of 
field soil may be determined by making a moisture test in the 
ordinary way for the total water contained,^ after the gravi- 

* A moisture determination on a sample of field soil is generally carried 
out as follows: — 100 grams of the sample, after thorough mixing, is 
weighed into a suitable weighing dish and air-dried. The sample is then 
placed in an oven and heated at 100°C or 110°C for four or five hours. 
It is then cooled in a disiccator and weighed. The loss in weight is 
water. The moisture is calculated as percentage based on the dry mat- 
ter of the soil. If the weight of the water lost was 20 grams, the 
percentage of moisture would be (20 -^ 80) X 100 or 25 per cent based 
on dry soil. 



162 NATURE AND PROPERTIES OF SOILS 

tational water has had time to drain away. This represents 
the hygroscopic plus the capillary water. A determination 
of the hygroscopic coefficient on another sample yields a figure 
which, when subtracted from the total water, will give the 
capillary water present in the soil. The capillary water at 
various points in a soil column may be obtained by subtracting 
the hygroscopic coefficient from the various percentages of 
moisture present, since the hygroscopic moisture is little in- 
fluenced by height of column or ordinary structural condi- 
tions. 

The determination cited above may or may not give the 
maximum water-holding capacity of a soil. To fill such a need 
a laboratory method has been devised by Hilgard,^ which 
attempts to show the maximum retentive power of a soil for 
water. 

A small perforated brass cup is used, having a diameter 
of about 5 centimeters and capable of containing a soil column 
1 centimeter in height. A short column is used, since it is 
only under such conditions that a soil may retain against 
gravity the greatest amount of water. Also the soil is able 
to expand or contract, as the case may be, on the assumption 
of water until an equilibrium is reached. A filter-paper disc 
is often placed in the metal cup, and the soil is poured in, 
gently jarred down, and stroked off level with the top of the 
cup. The cup is then set in water and the soil is allowed to 
take up its maximum moisture. After draining, the weight 
of the wet soil plus the cup, together with the weights pre- 
viously obtained, will allow a calculation of the total water 
retained based on the absolutely dry soil. If the maximum 
capillary water is desired, the hygroscopic coefficient may be 
subtracted from the maximum water retained. 

Since this method is a laboratory procedure and the soil 
used is not in its normal structural state, the results cannot 
be accurately applied to field conditions. While the figures 

» Hilgard, E. H., Soils, p. 209, New York, 1911. 



THE FORMS OF SOIL-WATER 163 

obtained may be fairly accurate for a sand, they are certainly 
much too high for heavy soils. Comparisons with field soils 
have shown the data obtained by the above method to be from 
30 to 130 per cent, too high.^ 

91. The capillary capacity of soils. — As might nat- 
urally be expected, the factors that tend to vary the amount 
of capillary water in a soil are several and their study is 
rather complex due to the secondary influences that they may 
generate and to the variable nature of the capillary moisture. 
These factors may be discussed under four heads: (1) surface 
tension, (2) texture, (3) structure and (4) organic matter. 

Any condition that will influence surface tension will ob- 
viously influence the forces active in the outer portion of the 
capillary water. A rise in temperature, for example, if the 
soil is capillarily saturated, will allow some of the water to 
become gravitational. A lowering of temperature would cause 
an opposite change. This theory has been verified by certain 
experiments by King,- in which he found, other conditions 
being constant, a very decided influence on capillary water 
through change of temperature. AVollny ^ has shown that a 
depression of .65 per cent, in sand to as high as 3.7 per cent, 
in kaolin may occur from a rise in temperature of twenty 
degrees. While surface tension may be greatly varied by the 
presence of salts in solution, the soil-water is generally so 
dilute that the condition is not very important * in determining 

* Alway, F. J., and McDole, G. R., The Fclation of Movement of 
Water in a Soil to its Hyqroscopicity and Initial Moistness; Jour. Agr. 
Ees., Vol. X, No. 8, pp. 391-428, 1917. 

Israelson, O. W., Studies on Capacities of Soils for Irrigation 
Water; Jour. Agr. Res., Vol. XIII, No. 1, pp. 1-36, 1918. 

^ King, F. H., Fluctuations in the Level and Bate of Movement of 
Ground Water; U. S. Dept. Agr., Weather Bur., Bui, 5, pp. 59-61, 
1892. 

' Wollny, E., Untersuchungen iiber die WasserJcapacitdt der Bodenarten; 
Forsch. a. d. Gebiete der Agri.-Physik, Band 9, Seite 361-378, 1886. 

* Karraker, P. E., Effect on Soil Moisture of Changes in the Surface 
Tension of the Soil Solution Brought About By Addition of SolublSi 
Salts; Jour. Agr. Ees., Vol. 4, No. 2, pp. 187-192, May, 1915. 



164 NATURE AND PROPERTIES OF SOILS 

capillary capacity except in arid or semi-arid regions. In 
fact, changes in surface tension through any cause are of little 
practical importance. 

The finer the texture of a soil the higher is its capillary 
capacity. This is due to the presence of colloidal material 
and to the greater number of angles in which capillary water 
may be held. The amount of .jnternal surface exposed by a 
fine-textured soil is immensely larger than in one of a sandy 
character. While texture influences both the inner and outer 
capillary water the structure of the soil has more to do with 
the active film-like portion. As a clayey soil is granulated 
the interstitial spaces are enlarged and an increased capillary 
capacity results. At the same time, compacting a sand will 
cause a rise in the capillary capacity of that^- soil by increasing 
not only the actual effective surface, but also the number of 
angles possible for capillary concentration. Further compact- 
ing will then cause a decrease. 

Organic matter, especially when well decayed, is commonly 
recognized as having great capillary capacity, far excelling 
the mineral portion of the soil in this respect. Its porosity 
affords an enormous internal surface, while its colloids exert 
an affinity for moisture which raises its water capacity to a 
very high degree. Its tendency to swell on wetting is but a 
change in condition incident to an approach to its maximum 
moisture content, and has a very marked influence on the 
structure of the soil. The water-holding capacity of muck 
and peat may range as high as 300 or 400 per cent, based on 
the dry matter present. Assuming a hygroscopic coefficient 
of 50 per cent., the capillary figure is still very high. Besides 
this direct effect, organic matter exerts a stimulus toward 
better granulation, a condition in itself favorable to increased 
water-holding power. 

The capillary water in any soil, other conditions being equal, 
tends to vary with the height of the column. This comes about 
from the effect of gravity on the outer portion of the capillary 



THE FORMS OF SOIL-WATER 



165 



film, tending to give more water at the 
base of the column. 

The condition may be explained em- 
pirically as follows : If a number of par- 
ticles carrying maximum capillary films 
are brought together vertically, the weight 
of a large portion of the conducting film 
is thrown momentarily on the surfaces at 
the top. The capillary spaces at this point 
immediately lose water downvvard, so that 
they may assume a greater curvature and 
thus support this extra weight thrown on 
them. This curvature must be sufficient to 
balance the curvature pressure of the par- 
ticles below plus the weight of the water 
in the connecting films. The particles be- 
neath are at the same time undergoing a 
similar adjustment with a set of particles 
farther below, losing water in order to 
allow a change of curvature. The action 
continues in this manner in an attempt to 
establish equilibrium, thus giving more 
water at the bottom of the column. If the 
amount of capillary water is too great to be 
supported, enough is lost by gravity to 
bring about an equilibrium (see Fig. 29). 

The above illustration, however, does not 
apply strictly to soil conditions, since only 
part of the capillary water is in a true film 
form and free to move with extreme ease. 
Moreover, rain water is applied from 
above, where also occurs rapid evaporation. 
Thus at any particular time the moisture 
content of a field soil might be higher near 
the surface than farther down in the soil 



Fig. 29. — Diagram 
showing in a con- 
ventional way 
the adjustment 
tendency of the 
outer capillary 
water in a long 
column and the 
appearance of 
free water if the 
weight is too 
great. 



166 



NATURE AND PROPERTIES OF SOILS 



or vice versa as the case may be. As the capillary water in a 
soil is reduced there is a tendency for the soil column to be 
more nearly uniform, providing, of course, that the equi- 
librium forces have had time to act and are not too much 
influenced by other factors. 

While representative data regarding the moisture-holding 
capacity of soils are difficult to give, the following figures 
from Always indicate the general effect of texture and organic 
matter. The maximum water capacity was determined in the 
laboratory and the maximum field capacity was obtained by 
sampling the soils very shortly after irrigation. 

Table XXXI 

THE MAXIMUM WATER CAPACITY OF VARIOUS SURFACE SOILS AS 

DETERMINED IN THE LABORATORY AND UNDER FIELD 

CONDITIONS, RESPECTIVELY " 



Soils 


Organic 
Matter 

% 


Hygro- 
scopic Co- 
efficient 

% 


Field 

Water 

Capacity 

% 


Maximum 

Water 

Capacity, 

Laboratory 

Method 

% 


Sand 


1.22 
1.07 
1.55 
4.93 
2.22 


1.1 
1.7 

3.3 
10.0 
10.1 
10.2 
12.9 


11.7 
12.8 
19.6 
31.5 
31.3 
39.2 
47.6 


37.0 


Sand 


27.1 


Sandy soil, residual. 
Red loam, residual . . 

Silt loam, loess 

Silt loam, loess 

Black adobe 


34.2 
49.0 
56.8 
60.9 
60.3 



The effect of texture on water capacity is very apparent, a 
rough correlation existing also between the water retained and 
the hygroscopic coefficient. The influence of organic matter 

^ Alway, F. J., and McDole, G. K., The delation of Movement of 
Water m a Soil to its Hygroscopicity and Initial Moistnessi; Jour. 
Agr. Ees., Vol. X, No. 8, pp. 391-428, 1917, 

* Note again that moisture percentages are always expressed on dry- 
soil weight. 



THE FORMS OF SOIL-WATER 



167 



is clearly shown by the two loess silt loams. Perhaps most 
important of all is the marked discrepancy between the actual 
field capacity and the arbitrary and artificial laboratory 
method. The normal water-holding capacity of a mineral soil, 
varying with texture and organic matter, seems to range from 





















Xv 


X 














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^N 














» >v 


S 














\ > 


. s 














40 \ 


\ \ 














t 


\^ 


\ 










C2 


% 














< 


^0 \ 


N 


. V 










H 


' t 




\ '' 










U 




\ 




\ 
\ 

\ 
\ 
\ 








1 


20 


\ 


N 


. \ 










\ 




\^ \ 












*x^ 




^>>^,^^\ 








o 






-ii/Jb 




V 








10 




*~" 





h-o^N 
















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<■• 


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tu 












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u 
Z 














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10 



15 



20 



25 



50 %WATER 



Fig. 30. — Diagram showing the distribution of moisture in capillary 
columns of soil of different textures. The end of each column 
rests in free water. (Buckingham, E., Bur. Soils, Bui. 38, 1907.) 

about 10 to 50 per cent, based on dry soil. Muck and peat of 
course run much higher, 400 per cent, being not uncommon.^ 

* Briggs and McLane have perfected a method of comparing soils on 
the basis of their capacity to hold water against a definite and constant 
centrifugal force of one to three thousand times the force of gravity. 
The soils, in thin layer, are placed in perforated brass cups which fit 
into a centrifugal machine capable of developing the above force, and 
are whirled until equilibrium is reached. The resultant moisture per- 
centage is designated as the moisture equivalent. It really represents 
the capillary capacity of a soil of minimum column length when subject 
to a constant and known force or pull. The finer the soil, the greater 
of course is the moisture equivalent. The authors found that 1 per cent. 
of clay or organic matter represented a retentive power of about .62 



168 



NATURE AND PROPERTIES OF SOILS 



92. Capillary movement of water. — It has already been 
shown that different thicknesses of capillary films tend to 
equalize in the soil due to the pulling forces developed by the 
angle of curvature between the particles.^ It is evident that 
differences in curvatures must be the motive force in the capil- 
lary movement of soil-water. Let it be supposed, for conveni- 
ence, that three equal spheres when brought in contact contain 
unequal amounts of water in the angles of curvature (see 
Fig. 31). In this case the greater pull would exist at A, since 
the angle here is more acute. Consequently water must move 

per cent., while 1 per cent, of silt corresponded to a retention of only 
.13 per cent, of water. Kepresentative data is as follows: 



Soils 



Norfolk coarse sand. . . 
Norfolk fine sandy loam. 

Yazoo loam 

Waverly silt loam 

Houston clay loam. . . . 
Houston clay 



Organic 

Matter 

% 



.9 
1.3 
1.3 
2.0 
3.7 
1.4 



Sands 


Silt 


Clay 


% 


% 


% 


87.9 


7.3 


4.8 


73.4 


18.1 


8.5 


25.8 


64.1 


10.1 


14.9 


62.9 


22.2 


30.9 


42.5 


26.6 


10.0 


56.6 


33.4 



Moisture 

Equivalent 

% 



4.6 
6.8 
18.9 
24.4 
32.4 
38.2 



Briggs, L. J., and McLane, J. W., The Moisture Equivalent of Soils; 
U. S. Dept. Agr. Bur. Soils, Bui. 45, 1907. 

^ An ingenious method for measuring quantitatively the capillary pull 
exerted by a moist soil has been devised by Lynde and Dupre. The 
apparatus consists of a glass funnel joined to a thick-walled capillary 
tube by means of a piece of rubber tubing, a water seal being used at 
this point. The lower end dips into mercury. The soil to be studied is 
placed in the funnel, and after being saturated is connected by means 
of a wick of cheesecloth or filter paper to the water column previously 
established in the capillary tube. If no break occurs between the soil 
and the capillary water column, the apparatus is ready for use. 

The excess water having drained away, there is a thinning of the films 
on the soil surface due to evaporation. Equilibrium adjustments now 
take place, which result in the drawing upward of the water column. 
The mercury follows, and the strength of the pull may be measured by 
the length of the mercury column. The old method of measuring capil- 
lary power by the water movement through a dry soil is vitiated by two 
conditions — the length of time necessary, and the fact that the maximum 
lift cannot be obtained due to excessive friction. This new method 
uses a wet soil, requires only a short time, and gives a more nearly 
accurate idea of the power of the capillary pull. It does not, however, 



THE FORMS OP SOIL-WATER 



169 



through the connecting film until the pull at A and that at B 
become the same. Such an adjustment might go on over a 
large number of films, and if one end of the column was ex- 
posed to an evaporation of just the correct rate and the other 
end was in contact witli plenty of moisture, large quantities 
of water would be moved by capillarity. 

This capillary movement may go on in any direction in the 
soil, since it is largely independent of gravity; yet under 
natural field conditions the adjustment tends to take place 
very largely in a vertical direction, due to evaporation and 
absorption by plants. When a soil is exposed to evaporation, 
the surface films are thinned and water moves upward to 
adjust the tension. This explains why such large quantities 
of soil-water may be lost so rapidly from an exposed soil. 
Capillary adjustment may go on downward, also, as is the 
ease after a shower. Here the rapidity of the adjustment is 
aided by gravity and movement of the water of percolation. 

The capillary adjustment in a soil tends to take place 
whether or not the soil column is in contact with free water. 
If no gravity water is present, the adjustment is merely from 
a moist soil to a drier one. In studying the rate and height 
of capillary movement of water in any soil, especially in the 



yield data regarding rate of movement, — a factor of vital importance 
to plant growth. 

Lynde and Dupre, in their results, confirm the statements already made 
regarding the relation of texture to capillary power : 



Soil 



Medium sand. . . 

Fine sand 

Very fine sand. 

Silt 

Clay 



Diameter op 

Grains in 
Millimeters 



.50 - .25 
.25 - .10 
.10 - .05 
.05 - .005 
.005- — 



Lift of Water 
Column, in Feet 



1.78 

4.05 

9.99 

26.80 



Lynde, C. J., and Dupre, H. A., On a New MetJiod of Measuring 
the Capillary Lift in Soils; Jour. Amer. Soc. Agron., Vol. 5, No. 2, 
pp. 107-116, 1913. 



170 NATURE AND PROPERTIES OF SOILS 

laboratory, the maintenance of a supply of free water is 
usually provided for, since this allows a nearer approach to 
the maximum capillary capacity for any point in the column 
and also gives the most rapid capillary adjustment. 

To persons familiar with the habits of growing plants, it is 
evident that capillary movement must play an important 
part in their nutrition, since the rootlets are unable to bring 
their absorptive surfaces in contact with all the interstitial 
spaces in which the bulk of the available water is held. Con- 
sequently a consideration of the movement of capillary mois- 




FiG. 31. — Conventional diagram showing the mechanics of the movement 
of the film portion of the capillary water. The readjustment takes 
place in the direction of (A) due to the tension developed by the 
greater film curvature at that point. 

ture is necessary, not only as to its mechanics, but also in 
respect to the factors influencing its rate and height of move- 
ment. These factors are as follows: (1) surface tension and 
viscosity; (2) thickness of capillary film; (3) texture; and 
(4) structure. 

Surface tension and viscosity. — As the force developed by 
surface tension is the activating factor in capillary adjust- 
ment, any change in the former will influence this movement. 
Theoretically, a rise in temperature or the presence of soluble 
salts would decrease the rapidity of the capillary activity of 
soil-water. In a normal soil, however, the change of surface 
tension is generally not sufficient to have any very great prac- 
tical influence. Viscosity, on the other hand, is much more 
important. If the viscosity of water at 0° C. is taken as 100, 



THE FORMS OF SOIL-WATER 171 

its viscosity at 25° is 50 and at 30°, 45. Tliis explains to a 
large degree the increased rate of capillary movement due to 
temperature rise.^ The distance of such adjustment would, 
however, be lessened somewhat. Salts in solution would tend 
to check the rate of capillary movement both through in- 
creased viscosity and the influence on surface tension.- It 
would only be in alkali soils, where the concentration of soluble 
salts is very great, that any considerable retardation would 
occur. 

Thickness of capillary film. — It has been repeatedly noticed, 
in the studj^ of the capillary adjustment between two soils 
that the lower the percentage of water, the slower is the move- 
ment. This indicates that the thickness of the outer capillary 
film, which connects the interstices in which lies the bulk of 
the movable soil-water, is an important factor in the rate of 
movement. 

The above phenomena may be empirically explained as fol- 
lows: Let it be supposed that a withdrawal of water occurs at 
A (see Fig. 32), the interstitial space between two of the 
particles, the water surface being represented by the line aa'. 
There is an immediate increase in the curvature of this sur- 
face, and water tends to flow through the capillary film chan- 
nel (cc'c'') toward this area of greater tension. If water 

* Bouyoucos has shown that the movement in a soil column of uniform 
moisture is from the warmer portion toward the colder. The movement 
from a moist layer to a dryer one goes on more rapidly than when the 
moist soil is cool and the dry soil warm. Bouyoucos, G. J., Effect of 
Temperature on Movement of Water Fapor and Capillary Moisture in 
Soils; Jour. Agr. Ees., Vol. V, No. 4, pp. 141-172, Oct., 1915. 

*Wollny, E., Untersuchungen iiber die Eapillare Leitung des Wassers 
in Boden. Forsch. a. d. Gebiete d. Agr.-Physik, Band 7, "Seite 269-308, 
1884. Also, Forsch. a. d. Gebiete d. Agri.-Physik, Band 8, Seite 206-220. 
1885. 

Briggs, L. J., and Lapham, M. H., Capillary Studies; U. S. Dept. 
Agr. Bur. Soils, Bui. 19, ppj. 5-18, 1902. 

Karraker, P. E., Eff'ect on Soil Moisture of Changes in the Surface 
Tension of the Soil Solution brought about by the Addition of Soluble 
Salts; Jour. Agr. Ees., Vol. IV, No. 2, pp. 187-192, May, 1915. 

Davis, E. O. E., The Eff'ect of Soluble Salts on the Physical Proper- 
ties of Soils; U. S. Dept. Agr. Bur. Soils, Bui. 82, pp. 23-31, 1911. 



172 



NATURE AND PROPERTIES OF SOILS 



continues to be withdrawn at A, this adjustment goes on with 
considerable ease until the film channel (cc'c'O becomes so 
thin as to cause its surface now (bb'b") to approach very 
closely to the surface of the soil particle and the inner capil- 
lary water. The sluggishness of the water movement becomes 
a factor at this point, impeding the capillary adjustment to- 
ward A. This point of sluggish capillary movement has been 
designated by Widtsoe^ as the point of lento-capillarity, and 




Fig. 32. — Conventional diagram for the explanation of the effect of the 
thickness of water film about the soil particles and their colloidal 
complexes on the ease of capillary adjustment. 

is expressed in percentage based on the dry weight of the 
soil. It lies near the transition zone between the inner and 
outer capillary water. 

The amount of capillary water delivered at any one point, 
therefore, will obviously be influenced by the thickness of the 
film and may consequently be taken as a measure of rate of 
adjustment. A short soil column should deliver more water 
than a longer one, due to the thicker films at the surface of 
the former. King,^ in studying the evaporation from the sur- 
faces of sand columns of different lengths, their bases being 
in contact with free water, obtained some significant data. 



^Widtsoe, J. A., and McLaughlin, W. W., The Movement of Water in 
Irrigated Soils; Utah Agr. Exp. Sta., Bui. 115, pp. 223-231, 1912. 

" King, F. H., Prvnciples and Conditions of the Movements of Ground 
Water; U. S. Geol. Survey, 19th Ann. Kept, Part II, p. 92, 1897- 
1898. 

Also Briggs, L. J., and Lapham, M. H., Capillary Studies; U. S. 
Dept. Agr. Bur. Soils, Bui, 19, pp. 24-25, 1902. 



THE FORMS OF SOIL-WATER 173 

He found, for example, that a six-inch column would deliver 
six times more water to its surface in a given time than a 
thirty-inch column operating under the same conditions. 

In air-dry soil it is obvious that, before capillarity may 
function, a continuous film must be present. Such a condi- 
tion is impossible unless some of the more active capillary 
moisture is in the soil. The water content in a soil must often 
be rather high before capillarity is a noticeable phenomenon. 
This condition is taken advantage of in the use of soil-mulches, 
where a loose dry layer of soil on the surface may check 
evaporation by impeding capillary rise. The presence of oily 
substances on the soil grains may also be of some importance 
in this respect. 

Texture. — In soils of fine texture not only is the amount 
of film surface exposed greater than in coarse soils but the 
curvature of the films is also greater, due to the shorter radii. 
The effective pressure exerted by the films is consequently 
much higher in fine-grained soil. Both the greater exposure 
of surface and the increased pressure serve to raise the fric- 
tion coefficient and retard the rate of flow. The finer the 
texture of the soil, other factors being equal, the slower is 
the movement of capillary water. Water should, therefore, 
rise less rapidly from a water-table through a column of clay 
than through a sand or a sandy loam. 

The distance to which water may be drawn by the effective 
capillary power of a soil, equilibrium being established, de- 
pends on the number of interstitial angles. The greater the 
number of angles, the greater is the total pulling power of 
the films. As a silt soil contains a larger number of such 
angles, its capillary pull is greater than that of sand, and con- 
sequently the ultimate movement would be of greater scope. 
The finer the texture, then, the slower is the rate of capillary 
movement but the greater is the distance. 

The relation of texture to rate and height of capillary move- 
ment in air-dry soil is shown by the following unpublished 



174 



NATURE AND PROPERTIES OF SOILS 



data, obtained in the laboratory of tbe Department of Soil 
Technology, Cornell University: 

Table XXXII 

EFFECT OF MOISTURE ON RATE AND HEIGHT OF CAPILLARY RISE 
FROM A WATER-TABLE THROUGH AIR-DRY SOIL 



SOIL 


1 
HouE 


1 
Day 


2 
Days 


3 

Days 


4 
Days 


5 

Days 


Sandy soil 

Clayey soil 

Silt loam 


Inches 
3.5 
.5 
2.5 


Inches 
5.0 
5.7 
14.5 


Inches 
5.9 
8.9 
20.6 


Inches 
6.8 
10.9 
24.2 


Inches 

6.8 

12.2 

26.2 


Inches 
6.9 
13.3 
27.4 



It is seen that the movement in sand is rapid, one-half of 
the total rise being attained in one hour. The maximum 
height is reached in about three days. The silt loam in this 
case seems to be of just about the proper textural condition 
for a fairly rapid rise, yet it exerts enough capillary pull to 
attain a good distance above the water-table. The friction 
in the clay is greater, however, and this results in a slower 
rate. 

Structure has already been shown to affect capillary capac- 
ity by its influence on the angle interstices and the closeness 
of the contacts. Evidently, therefore, it may alter both the 
rate and the height of capillary rise. The loosening of a clay 
soil or the compacting of a sandy soil will lessen the effective 
film friction, while at the same time it may strengthen the 
capillary pull resulting in a faster and a higher capillary flow 
of water. What may be the best structural condition of any 
soil in which this result is realized to its highest degree can 
not be predicted exactly. In general, however, this point is 
approached when the soil is in the best physical condition for 
crop growth. Tillage operations, tile drainage, and the addi- 
tion of lime and organic matter operate toward this result by 
their granulating tendencies; while rolling, by compacting a 



THE FORMS OF SOIL- WATER 175 

too loose .surface, may accomplish the same effect but by an 
opposite process. 

At certain seasons of the year capillarity should be im- 
peded near the surface, as it continually carries valuable 
water upward to be lost by evaporation. Tliis movement may 
be checked somewhat by producing on the soil surface, by 
appropriate tillage, a layer of dry, loose soil. This layer, called 
a soil-mulch, resists wetting because of its dryness, while at 
the same time it affords but little surface and few angle inter- 
stices for effective capillary pull. Moisture also moves very 
slowly from a moist, cool soil to a dry, warm one.^ Thus it is 
that a farmer, in order to meet immediate or future plant 
needs, may alter and control capillary movement by careful 
attention to physical conditions, especially those at the sur- 
face where evaporation is always active. 

93. Gravitational water and its movement. — As soon 
as the capillary capacity of a soil column is satisfied, further 
addition of moisture will cause the appearance of free water 
in the air spaces. By the attraction of gravity, this water 
moves forward through the soil at a rate varying with con- 
ditions. In general, the flow is governed by four factors — 
pressure, temperature, texture, and structure. An under- 
standing of the operation of these forces is important, since 
the rapid elimination of free water from the soil is necessary 
for normal plant growth. 

It is very evident that any pressure exerted on a water 
column will alter the rate of flow. Under normal conditions 
pressure may arise from two sources, atmospheric pressure 
and the weight of the water column. Changes in barometric 
pressure are communicated to gravitational water through a 
movement of the soil-air. As the mercury column rises more 
air is forced into the soil and the pressure on the soil-water 

^ Bouyoueos, G. J., Effect of Temperature on Movement of Water 
Vapor and Capillary Moisture in Soils; Jour. Agr. Ees., Vol. V, No. 4, 
pp. 141-172, Oct., 1915. 



176 NATURE AND PROPERTIES OF SOILS 

increases. The weight of tlie free water column may also 
have some influence. Although King^ and Welitschkowsky- 
have shown that definite relationships exist between the move- 
ment of gravity water and both atmospheric pressure and 
weight of water column, the practical field importance of these 
factors are rather slight. 

A rise in temperature of the soil not only varies the relative 
amounts of capillary and free water present, but at the same 
time it increases the fluidity and thus facilitates percolation. 
The expansion of the soil-air also tends to increase such 
movement. On the other hand the swelling of hydrogels 
which may be present tends to impede percolation to such an 
extent that the movement of free water through a heavy soil 
is often markedly checked by temperature rise. 

Of much more practical importance than either pressure 
or temperature in the flow of gravity water is the texture and 
the structure of the soil. In working with sands of varying 
grades, Welitschkowsky,^ WoUny,* and others have shown that 
the flow of water varies with the size of particle, or texture. 
King ^ has demonstrated that in general the rate of flow 
through such is directly proportional to the square of the 
diameter of the particles. By the use of the effective mean 

' King, F. H., Principles and Conditions of the Movements of Ground 
Water; U. S. Geol. Survey, 19th Ann. Dep^., Part II, pp. 67-206; 1897- 
1898. 

King, F. H., The Soil, p. 180, New York, 1906. 

*Welitschkowsky, D. von., Experimentelle untersuchungen iiber die 
Permeabilitdt des Bodens fiir Wasser; Archiv. f. Hygiene, Band II, 
Seite 499-512. 1884. 

WoUny, E., Untersuchungen iiber die Permeabilitdt des Bodens fiir 
Wasser; Forsch. a. d. Gebiete d. Agr.-Physik, Band 14, Seite 1-28, 1891. 

" Welitschkowsky, D. von., Experimentelle untersuchungen iiber die 
Permeabilitdt des Bodens fiir Wasser; Archiv. f. Hygiene, Band II, 
Seite 499-512, 1884. 

* WoUny, E., Untersuchunger iiber den Einfluss der StruMur des 
Bodens auf dessen Feuchtighetis — und Temperaturverhaltnisse ; Forsch. 
a. d. Gebiete d. Agr.-Physik, Band 5, Seite 167, 1882. 

"King, F. H., Principles and Conditions of the Movements of Ground 
Water; U. S. Geol. Survey, 19th Ann. Rep., Part II, pp. 222-224, 1897- 
1898. 



THE FORMS OF SOIL-WATER 177 

diameter of a sand sample he was able to calculate a theo- 
retical flow which compared very closely to observed percola- 
tions. In sandy soils low in organic matter this law holds 
in a very general way, but in clays it fails entirely. For 
example, if such a law was in force a sand having a diameter 
of .5 millimeter would exhibit a flow 10,000 times greater 
than that through a clay loam with a diameter, say, of .005 
millimeter; whereas the actual ratio, as observed experimen- 
tally by King, was less than 200, Such a discrepancy is to be 
expected as it is impossible accurately to apply mathematics 
to soils carrying any appreciable amount of colloidal matter. 

Evidently, therefore, while it can be stated as a general 
thesis that the flow of gravity water varies with the texture, 
being much more rapid through a coarse than through a fine 
soil, no law can be deduced for soils, since structure 
exerts such a modifying influence. The percolation in a 
heavj' soil takes place largely through lines of seepage, which 
are really large channels developed by various agencies. 
If in the drainage of average soil, the farmer depended on the 
movement of water through the individual pore spaces, the 
soil would never be in condition for crop growth. These lines 
of seepage are developed by the ordinary forces that function 
in the production of soil granulation, as freezing and thawing, 
wetting and drying, lime, organic matter, roots, and tillage 
operations. 

94. Determination of the quantity of free water that 
a soil v^ill hold. — While there is no particular advantage 
in finding the quantity of gravitational water that a soil will 
hold, since a normal soil should never remain saturated for 
any length of time, it is nevertheless of interest to know by 
what means such data may be obtained. One method is to 
saturate a soil column of known weight, and then, by exposing 
it to percolation, measure the amount of water that is lost. 
The gravitational water can then be expressed in terms of dry 
soil. 



178 NATURE AND PROPERTIES OF SOILS 

As valuable a figure may be obtained by calculation, pro- 
viding the specific gravity and volume weight of the soil is 
known together with its percentage of moisture based on dry 
weight when it is capillarily satisfied. The following formu- 
Iffi ^ may be used : 

Tvol. wt. 



1. Percentage pore space = 100 



iOO] 



Lsp. gr. 

2. Percentage free water = % Pore Space _ ^^ ^^^^^ ^^ 

(based on dry weight ^^^- ^^- maximum 

of soil) capillarity 

Suppose, for example, that a sand with a specific gravity of 
2.6 and a volume weight of 1.56 contains 20 per cent, of water 
when at its maximum retentive power. Its pore space would 
be 40 per cent. If this pore space were filled with water, the 
soil would contain 25.6 per cent, based on the dry weight of 
the soil (per cent, pore space -=- vol. wt.). If the total capac- 
ity of the soil for water is 25.6 per cent, and the hygroscopic 
plus the capillary capacity is 20 per cent., the free Avater must 
be 5.6 per cent.^ 

95. Importance of the study of the flow and composi- 
tion of drainage water. — A clear understanding of the 
factors governing the flow of gravitational water is of special 
importance in tile drainage operations, particularly regarding 
the depth of and interval between tile drains. Since percola- 
tion is so slow in a heavy soil it is evident that the tile must 
be near the surface in order to secure efficient drainage. In 
a sand the depth may be increased, because of the slight re- 

^ Percentage of pore space represents the percentage of water by 
volume that would occupy such a space. Percentage of water by volume 
divided by volume weight gives percentage of water based on dry weight 
of soil. Conversely, multiplying percentage of moisture calculated on 
dry weight of soil by volume weight will give percentage of water by 
volume. 

The air space in a soil at any particular moisture content may be cal- 
culated as follows: 

Percentage of air space = % pore space — (%H20 X Vol. Wt.) 

^ Below will be found some generalized moisture data on two distinct 



THE FORMS OP' SOIL-WATER 179 

sistance offered to water movement. The depths for laying tile 
in a heavy soil range from one and a half to two and a half 
feet, while in a sand the tile may often be placed as deep as 
four feet below the surface. It is evident also that the less 
deep a tile drain is laid the less distance on either side it will 
be effective in removing the water; consequently on a clay 
soil the laterals must be relatively close as compared to the 
interval generally recommended for a sandy soil. A rational 
understanding of the movements of gravitation water is 
clearly necessary in the installation of tile drains not only 
that the system may be efficient, but also that a minimum 
effective cost may be realized.^ 

The water lost from the soil by drainage is of especial in- 
terest in plant production because of the large amounts of 
nutrient elements carried away each year. Such loss is par- 
ticularly important in regard to the lime and nitrogen.- The 
equivalent of approximately 500 pounds of sodium nitrate 
and 1000 pounds of calcium carbonate have been known to 
leach from an acre of bare soil every year under humid con- 
ditions. 

classes of soils. As usual, all of the moisture data is expressed as per- 
centage based on absolutely dry soil. 

Sandy Clayey 
Soil Soil 

Specific gravity 2.67 2.65 

Volume weight 1.60 1.20 

Pore space 40.0% 54.8% 

Hygro. coefficient 1.0% 10.0% 

Optimum moisture (average) 10.0% 30.0% 

Maximum field capacity 17.0% 44.0% 

Air space at hygro. coefficient 38.4% 42.8% 

Air space at opt. moisture 24.0% 18,7% 

Air space at max. field capacity 12.8% 1.9% 

Possible free water 8,0% 1.6% 

See Kopecky, J., Die physilcalischen Eigenschaften des Boden; 
Internal Mitt f. Bodenkunde, Bd. IV, Heft 2-3, Seite 138-180. 1914. 

^ For a more complete discussion of tile drains, see Chap. X, para- 
graph 110. 

'Lyon, T, L., and Bizzell, J, A,, Lysimeter Experiments; Cornell 
Univ, Agr. Exp. Sta., Memoir 12, June, 1918. 



180 NATURE AND PROPERTIES OF SOILS 

Two methods of procedure are available for the study of 
drainage problems — the use of an efficient system of tile 
drains, and the construction of lysimeters. For the first 
method an area should be chosen where the tile drain receives 
only the water from the area in question and where the drain- 
age is efficient. A study of the amounts of flow throughout 
a term of years will yield much valuable data concerning the 
factors already discussed. An analysis of the drainage water 
will throw light on the ordinary losses of plant nutrients from 
a normal soil under a known cropping system. The advantage 
of such a method of attack lies not only in the fact that a 
large area of undisturbed soil is considered, but also in the 
opportunity to study practical field treatments in relation to 
the movement and composition of drainage water. 

The lysimeter method, however, has been the usual mode of 
approaching such problems. In this method a small block of 
soil is used, being entirely isolated by appropriate means from 
the soil surrounding it. Effective and thorough drainage is 
provided. The advantages of this method are that the varia- 
tions in a large field are avoided, the work of carrying on the 
study is not so great as in a large field, and the experiment 
is more easily controlled. One of the best-known sets of lysi- 
meters is that at the Rothamsted Experiment Station^ in Eng- 
land. Here blocks of soil one one-thousandth of an acre in 
surface area were isolated by means of trenches and tunnels, 
and, supported in the meantime by perforated iron plates, 
were permanently separated from the surrounding soil by 
masonry. The blocks of soil were twenty, forty, and sixty 
inches in depth, respectively. Facilities for catching the drain- 
age were provided under each lysimeter. The advantages of 
such a method of construction lies in the fact that the struc- 
tural condition of the soil is undisturbed and consequently the 
data are immediately trustworthy. 

*Lawes, J. B., Gilbert, J. H., and Waring^ton, R., On the Amount 
and Composition of the Bain and Drainage Waters Collected at Bothar.i- 
sted; Jour. Roy. Agr. Soc, Ser. II, Vol. 17, pp. 269-271, 1881. 



THE FORMS OF SOIL-WATER 



181 



At Cornell University^ a series of cement tanks sunk in 
the ground have been constructed. Each tank is about four 
feet and two inches square and about four feet deep. A slop- 
ing bottom is provided, with a drainage channel opening into 



<^i^ 







'^^^//A^-r<^^^^<^///d0'^ 



-o A O 



Fig. 



33. — Cross section of the lysimeter tanks at Cornell University, 
Ithaca, New York. Each tank is one of a series, one tmiHel serving 
the two rows. Dimensions are given in feet and inches. Soils under 
investigation (a), outlet (p), can for catching drainage water (c) 
and sky-light (w). 



a tunnel beneath and at one side. As the tanks are arranged 
in two parallel rows, one tunnel suffices for both. (See Fig. 
33.) The sides of the tanks are treated with asphaltum in 

^ Lyon, T. L,, Tanks 'for Soil Investigation at Cornell University; 
Science, N. Ser., Vol. 29, No. 746, pp. 621-623, 1909. 

There are other types of lysimeters. See, for example, Mooers, C. A., 
and Maclntire, W. H., Two Equipments for Investigation of Soil Leach- 
ings: I. A Pit Equipment. II. A Hillside Equipment; Tenn. Agr. Exp. 
Sta., Bui. Ill, 1915. 

Maclntire, W. H., and Mooers, C. A., A Pitless Lysimeter Equip- 
ment; Soil Sci., Vol. XI, No. 3, pp. 207-209, Mar., 1921. 



182 NATURE AND PROPERTIES OF SOILS 

order to prevent solution. The soil must of course be placed 
in the tanks, this causing a disturbance of its structural con- 
dition. As a consequence, data as to rate of flow and com- 
position of the drainage water are rather unreliable for the 
first few years. Such an experiment must necessarily be of 
considerable duration. 

96. Thermal movement of water. — Little has been said 
as yet regarding this mode of water movement, the vapor 
flow, which is not peculiar to one form of soil-water but affects 
them all. It is at once apparent that the movement of water- 
vapor can be of little importance within the soil itself, since 
it depends so largely on the diffusion and convection of the 
soil-air. While the soil-air is no doubt practically always 
saturated with water-vapor, the loss of moisture by this means 
is slight. Buckingham ^ has shown that, while sand allows 
such a movement to the greatest degree, the loss through any 
appreciable depth of layer is almost negligible. The question 
of the thermal movement of water at the soil surface, however, 
is vital in farming operations. At this point the moisture is 
exposed to sun and wind, and drying goes on rapidly, the free, 
capillary, and a part of the hygroscopic water vaporizing in 
the order named. If the loss of the moisture in the surface 
layer of soil was the only consideration, the problem would 
not be serious; but the movable water of the whole soil sec- 
tion must be considered also. As the films at the surface be- 
come thin, a capillary movement begins, and if the evapora- 
tion is not too rapid a considerable loss of water may occur in 
a short time. The moisture thus lost is that of most value 
to plants. The evaporation from the bare soil in the Rotham- 
sted lysimeters^ averaged about seventeen inches a year, with 

^ Buckingham, E., Studies on the Movement of Soil Moisture; U. S. 
Dept. Agr. Bur. Soils, Bui. 38, pp. 9-18, 1907. 

See also Bouyoucos, G. J., Effect of Tem^perature on Movement of 
Water Vapor and Capillary Moisture in Soils; Jour. Agr. Ecs., Vol. V, 
No. 4, pp. 141-172, Oct., 1915. 

=" Warington, R., Physical Properties of the Soil, p, 109; Clarendon 
Press, Oxford, 1900. 



THE FORMS OF SOIL-WATER 183 

a rainfall ranging from twenty-two to forty -two inches. This 
means that from one-third to one-half of the effective 
rainfall was entirely lost as thermal water. The necessity of 
checking such a loss becomes apparent, especially in regions 
where rainfall is slight or drought periods are likely to occur. 
As no country is free from one or the other of such con- 
tingencies, the great prominence that methods of moisture 
conservation hold in systems of soil management is under- 
standable. While means of checking losses by leaching and 
run-off are advocated, effective retardation of surface evapora- 
tion is always emphasized. 



CHAPTER IX 

THE WATER OF THE SOIL IN ITS RELATION TO 
PLANTS 

Water begins its service to plants by promoting the proc- 
esses of soil weathering, which results in the simplification of 
compounds for plant utilization. It also functions more di- 
rectly in plant development in maintaining the turgidity of 
the cells, in carrying materials, regulating temperature and 
in furnishing a supply of hydrogen and oxygen for the plant. 
These direct and indirect functions of water in relation to 
plant growth may be considered from a number of different 
viewpoints. 

97. Functions of water to plants. — Water acts as a 
solvent and as a medium for the transfer of nutrients from 
the soil to the plant. This transfer relationship is rather 
complex, since most nutrient materials penetrate the cell-walls 
of the absorbing surfaces of the roots in an ionic condition. 
As a nutrient water becomes a part of the cell contents with- 
out change or is broken down into its elements and utilized in 
the production of new compounds. In addition, water by 
maintaining turgidity, in equalizing the temperature by evap- 
oration from the leaves, and in facilitating quick shifts of 
nutrients and food from one part of the plant to another, 
acts as a carrier during assimilation and while synthetic and 
metabolic processes are going on. 

Soil-moisture, therefore, in proper amounts, becomes one 
of the controlling factors in crop growth and must be looked 
to before the maximum utilization of the nutrient elements 
can be expected. The amount of water held within the plant 

184 



WATER OF SOIL IN ITS RELATION TO PLANTS 185 

is not large, however, in comparison with the amount lost 
by transpiration, although green plants contain from 60 to 
90 per cent, of moisture. 

Because of the readiness with which moisture passes from 
plants into the atmosphere, large quantities must be taken 



16 



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Fig. 34. — The effect of increasing water supply on the production of dry- 
matter in various crops. The water is expressed in acre-inches. 



from the soil in order that the plant may maintain its proper 
turgor. That the crop may be properly supplied with water, 
optimum moisture conditions should prevail in the soil at 
all times during the growing season. It must not be inferred 
that loss through the plant is the only means by which mois- 
ture leaves the soil, since drainage and evaporation are by 
no means insignificant factors. 



186 



NATURE AND PROPERTIES OF SOILS 



98. Influence of water on the plant.^ — As the amount 
of water available to a crop is increased up to a certain point, 
the vegetative growth also is usually increased, the plant be- 
coming more succulent. The percentage of moisture in the 
crop, even at harvest time, is usually high. Shipping qualities 
are depressed with increased moisture, especially if the water 
available is excessive. With an enlargement of the plant 
cell a change probably occurs in the cell contents, tending 
toward a greater susceptibility to disease. 

Ripening especially is delayed by large amounts of mois- 
ture, tillering is diminished, and the percentage of protein 
content of the crop is decreased. It is a curious fact that 
many of the general and morphological effects of large quan- 
tities of available water on plant growth are the same as those 
caused by the presence of too much soluble nitrogen. In 
cereals the stimulation from a large supply of water is 
shown especially in the ratio of grain to straw. Widt- 
soe's^ findings in this regard are representative of the data ^ 
available on this point: 

Table XXXIII 

DISTRIBUTION OF DRY MATTER BETWEEN GRAIN AND STRAW WITH 
VARYING AMOUNTS OF WATER. 



Inches of water ap- 
plied 

Grain in percentage 
of dry matter of 
entire crop .... 




50 



33 



' Mitscherlich, E. A., Das Wasser als Fegetationsfaltor; Landw. Jahr., 
Band 42, Seite 701-717, 1912. 

^Widtsoe, J. A., The Production of Dry Matter with Different Quan- 
tities of Irrigation Water; Utah Agr. Exp. Sta., Bui. 116, p. 49, 1912. 

' Bunger, H., Jjher den Einfluss Ferschieden Hohen Wasser gehalts des 
Bodens in den Einzelhen Vegetationsstadien bei Versehiedenem Nahr- 
stoffreichtum auf die Entivicl-hing des Haferp flans en; Landw. Jahrb., 
Band 35, Seite 941-10.51, 1906. 

Also, Seelhorst, C, von, und Freckmann, W., Der Einfluss des Was- 
sergehaltes des Bodens auf die Ernten und die Ausbilding V erschiedener 
Getriedevarietdten ; Jour. f. Landw., Band 51, Seite 253-269, 1903. 



WATER OF SOIL IN ITS RELATION TO PLANTS 187 

As a rule, this depression of the ratio of grain to straw is 
not due to an actual decrease in the grain, but to a corre- 
spondingly greater production of dry matter in the vege- 
tative parts. As available water is augmented, the dry mat- 
ter of plants increases until a maximum is reached. The gen- 
eral relationships are well exemplified by data from AVidtsoe ^ 
(Fig. 34), although other equally valuable figures may be 
obtained from von Seelhorst - and Atterberg,=* who have done 
much work on the subject. 

99. The water requirements of plants. — As might be 
expected, the pounds of water transpired for every pound of 
dry matter produced in the crop is very large. This figure, 
called the transpiration ratio, or water requirement, ranges 
from 200 to 500 for crops in humid regions, and almost twice 
as much for crops in arid climates. An accurate determina- 
tion of the transpiration ratio of a crop is somewhat difficult, 
due to the methods of procedure necessary and also to the 
difficulty of controlling the numerous factors that influence 
the transpiration. For really reliable figures the plants must 
be grown in cans or pots in order that the water lost may 
be determined accurately by weighing. If there is no percola- 
tion the water ordinarily lost from a cropped soil includes 
both that evaporated from the soil surface and that tran- 
spired from the leaves. The former loss may be controlled 
largely in one of two ways: (1) by covering the soil so that 
evaporation is absolutely checked and the only loss is by 
transpiration; or (2) by determining the evaporation from a 
bare pot and, by substracting this from the total water loss 

^Widtsoe, J. A., The Production of Dry Matter with Different Quan- 
tities of Irrigation Water; Utah Agr. Exp. Sta., Bui. 116, pp. 19-25, 
1912. 

' Seelhorst, C, von, und Krzymowski, E., Versuch iiber den Einfluss, 
welehen das Wasser in dem Verschiedenem V egetationsstadien des Hafers 
auf sein Waclistum ausiibt; Jour. f. Landw., Band 53, Seite 357-370, 
1905. 

^Atterberg, A., Die Variationem der Ndhrstoffgehalte bei dem Safer; 
Jour. f. Landw., Band 49, Seite 97-113, 1901. 



188 NATURE AND PROPERTIES OF SOILS 

from a cropped soil, finding the loss due to transpiration 
alone. 

An objection to the former method is that any covering 
which interferes with evaporation interferes with proper soil 
aeration also and may render soil conditions abnormal. In 
the second method, however, an even more serious error en- 
ters, since the evaporation from the bare soil is not the same 
as that from a soil covered by vegetation because of the effect 
of shading. Moreover, due to the action of the roots, less 
water is likely to move to the surface by capillary attraction 
in the cropped soil. Therefore any data that may be quoted 
can be only general in its application, not only because of the 
errors of determination but also because of the great num- 
ber of factors that under normal conditions may vary the 
transpiration ratio. The following data drawn from various 
investigators working by the general methods ^ already out- 
lined, give some idea of the water transpired by different 
crops, due allowance being made for various disturbing fac- 
tors. (See Table XXXIV, page 189.) 

100. Factors affecting transportation. ^ — It is obvious 
from the figures quoted that the transpiration ratio of a crop 
is the resultant of a number of influences.^ The factors may 
be listed under three heads, as follows : 

1. Crop. — Difference due to different crops and to vari- 
ations of the same crop. 

^A brief discussion of the various methods is found as follows: 

Montgomery, E. G., Methods of Determining the Water Eequire- 
ments of Crops; Proc. Amer. Soe. Agron., Vol. 3, pp. 261-283, 1911. 

Also Briggs, L. J., and Schantz, H. L., The Water Bequirement of 
Plants; U. S. Dept. Agr., Bur. Plant Ind., Bui. 285, 1913. 

^ Kiesselbach, T. A., Transpiration as a Factor in Crop Production; 
Nebr. Agi-. Exp. Sta., Res. Bui. 6, June, 1916. 

'A complete review of the literature concerning the climatic and 
soil factors in their effect on transpiration may be found as follows: 
Briggs, L. J., and Shantz, H. L., The Water Bequirement of Plants; 
U. S. Dept. Agr., Bur. Plant Ind., Bui. 285, 1913. 

See also, Briggs, L. J., and Shantz, H. L,, Daily Transpiration dur- 
ing the Normal Growth Period arid its Correlation with the Weather; 
Jour. Agr. Res., Vol. VII, No. 4, pp. 155, 212, Oct., 1916. 



WATER OF SOIL IN ITS RELATION TO PLANTS 189 



Table XXXIV 

WATER REQUIREMENTS OF PLANTS AS DETERMINED BY DIFFER- 
ENT INVESTIGATORS. 



Crop 


Lawes ^ 
Harpen- 

DEN, 

England, 
1850 


Wollny ' 

Munich, 

Germany 

1876 


Hell- 

RIEGEL * 

Dahme, 

Germany 
1883 


- 

King* 

Madison, 
Wis., 1895 


Leather " 

PUSA, 

India 
1911 


Briggs 

AND 

Shantz' 

Akron, 

Colo. 

1911-1913 


Barley . . . 
Beans . . . . 
Buckwheat 
Clover . . . 
Maize .... 
Millet .... 

Oats 

Peas 

Potatoes . . 
Rape . . . . 

Rye 

Wheat ... 


258 
209 

269 
259 
247 


774 

646 

233 
447 
665 
416 

912 


310 

282 
363 
310 

376 
273 

353 
338 


464 

576 
271 

503 
477 

385 


468 

337 

469 
563 

- 

544 


534 
736 
578 
797 
368 
310 
597 
788 
636 
441 
685 
513 



^ Lawes, J. B., Experimental Investigation into the Amount of Water 
Given off by Plants during their Growth; Jour. Hort. Soc, London, 
Vol. 5, pp. 38-63, 1850. Pots holding 42 pounds of field soil were used. 
Evaporation from soil was reduced to a very low degree by perforated 
glass covers cemented on the pots. The figures quoted are from un- 
fertilized soil. 

* Wollny, E., Der Einfluss der Pflanzendecke und Beschattung auf die 
Physil-alischen Eigenschaften und die Fruchtharlceit des Bodens, Seite 
125 ; Berlin, 1877. Wollny grew plants in sand in amounts ranging 
from 5 to 12 kilograms. Evaporation was reduced to a very low 
degree by perforated covers. Actual evaporation from uncropped cans 
was observed, however. 

^ Hellriegel, H., Beitrdge zur den NaturwissenschaftUchen Grundlagen 
des Ackerhaus, Seite 663; Braunschweig, 1883. Hellriegel grew plants 
in 4 kilograms of clean quartz sand and supplied them with nutrient 
solutions. The loss by evaporation from uncropped pots was used in 
determining losses by transpiration. In later experiments covers were 
used in order to cut down evaporation. 

*King, F. H., Physics of Agriculture, p. 139; published by author, 
Madison, Wis., 1910. Also, The Number of Inches of Water Required 
for a Ton of Dry Matter in Wisconsin; Wis. Agr. Exp. Sta., 11th Ann. 
Rep., pp. 240-248, 1894; and The Imyortance of the Bight Amount and 
Might Distribution of Water in Crop Production; Wis. Agr. Exp. Sta., 



190 NATURE AND PROPERTIES OF SOILS 

2. Climate — Rain, humidity, sunshine, temperature, and 
wind. 

3. Moisture and fertility,^ 

Not only do different plants ^ show a variation of transpira- 
tion the same season, but the same plant may give a totally 
different transpiration in separate years. This is due in part 
to inherent differences in the plant itself. For example, the 
extent of leaf surface or root zone would materially influence 
the transpiration relationship under any given condition. 
However, a great deal of the variation observed in the ratios 
already quoted arises from differences in climatic conditions. 
As a general thing, the greater the rainfall the higher is 
the humidity and the lower is the relative transpiration. 
This accounts for the high figures obtained by Widtsoe ' in 
Utah. Montgomery * found, in studying the water require- 

^ Fertility is used here in the sense of potential productivity. It 
refers especially to the ultimately available nutrients of the soil. 

' Miller, E. C, and Coffman, W. B., Comparative Transpiration of 
Corn and the Sorghums; Jour. Agr, Ees., Vol. XIII, No. 11, pp. 579- 
604, June, 1918. 

'Widtsoe, J. A., The Production of Dry Matter with Different Quan- 
tities of Irrigation Water ; Utah Agr. Exp. Sta., Bui. 116, 1912. Also, 
Irrigation Investigations. Factors Influencing Evaporation and Trans- 
piration; Utah Agr. Exp«. Sta., Bui. 105, 1909. 

* Montgomery, E. G., and Kiesselbach, T. A., Studies in Water Re- 
quirements of Corn; Nebr. Agr. Exp. Sta., Bui. 128, p. 4, 1912. 

14th Ann. Eep., pp. 217-231, 1897. King used cans holding about 400 
pounds of soil. Some were set down into the earth while others were 
not. Part of the work was carried on in the field; the remainder was 
run in vegetative houses. Normal soils were used. Evaporation from 
soil was very low, water being added from beneath. The data quoted 
are the average of a large number of tests. 

® Leather, J. W., Water Requirements of Crops in India; Memoirs, 
Dept. Agr., India, Chem. Series, Vol. I, No. 8, pp. 133-184, 1910, and 
No. 10, pp. 205-281, 1911. Jars containing from 12 to 48 kilograms 
of soil were used. Loss by evaporation was determined on bare pots. 
The plants were grown in culture houses or in screened inclosures. 

*Briggs, L. J., and Schantz, H. L., Relative Water Requirement of 
Plants; Jour. Agr. Eesearch, Vol. Ill, No. 1, pp. 1-63, 1914. Also, 
The Water Requirements of Plants; U. S. Dept. Agr., Bur. Plant Ind., 
Bui. 284, 1913. Plants were grown in cans holding 250 pounds of soil. 
Evaporation from soil was prevented by means of a paraflSn covering. 
Work was conducted in screened inclosures. The data are the average 
of several years' work. 



WATER OF SOIL IN ITS RELATION TO PLANTS 191 

ments of corn under greenhouse conditions, that an increase 
in the percentage humidity from 42 to 65 lowered the 
transpiration ratio from 340 to 191. In general, temperature, 
sunshine, and wind vary together in their effect on transpira- 
tion. That is, the more intense the sunshine, the higher is 
the temperature, the lower is the humidity, and the greater 
is likely to be the wind velocity. All this would tend to raise 
the transpiration ratio. 

From the soil standpoint, however, the factors inherent 
in the soil itself are of more vital importance as regards tran- 
spiration, since they can be controlled to a certain extent un- 
der field conditions. An increase in the moisture content of a 
soil usually results in an increased transpiration ratio. The 
work of Ilellriegel ^ with barley grown in quartz sand con- 
taining a nutrient solution may be cited in this regard, to- 
gether with the data obtained by Montgomery ^ at Lincoln, 
Nebraska, with maize grown in a loam soil : 

Table XXXV 

EFFECT OF SOIL-MOISTURE ON TRANSPIRATION. 



Barley — Hellriegel 


Maize — Montgomery 


SOIL-MOISTURE 

PERCENTAGE 

OF TOTAL 

CAPACITY 


TRANSPIRATION 
RATIO 


soil-moisture 

percentage of 

total capacity 


transpiration 
ratio 


80 
60 
40 
30 
20 
10 


277 
240 
216 
223 
168 
180 


100 
80 
60 
45 
35 


290 
262 
239 
229 
252 



^ Hellriegel, H., Beitrdge zu den N aturwissenschaftlicTien Grundlage 
des Aclerbmts, Seite 629, Braunschweig, 1883. 

* Montgomery, E. G., Methods of Determining^ the Water Bequire- 
ments of Crops; Proc. Amer. Soc. Agron., Vol. 3, p. 276, 1911. 



192 



NATURE AND PROPERTIES OF SOILS 



These data show clearly that an excessive amount of mois- 
ture in the soil is not a favorable condition for the economical 
use of water. 

The amount of available nutrients is also concerned in the 
economic utilization of water. In general the data along 
these lines show that the more productive the soil the lower 
is the transpiration ratio. Therefore, a farmer, in raising 
the productivity of his soil by drainage, lime, good tillage, 
green-manures, barnyard manures, and fertilizers^ provides 
at the same time for a greater amount of plant production 
for every unit of water utilized. The total quantity of water 
taken from the soil, however, will probably be larger. 

The following figures from Montgomery ^ are representative 
of data available on this phase : 



Table XXXVI 

RELATIVE WATER REQUIREMENT OF MAIZE ON DIFFERENT TYPES 
OF NEBRASKA SOILS, 1911. 



Soil 


Dry Weight of Plants 
IN Grams per Pot 


Transpiration Ratio 




MANURED 


UNMANUEED 


MANURED 


unmanured 


Poor (15 bushels) . . . 
Medium (30 bushels) 
Fertile (50 bushels) . 


376 
413 
472 


113 
184 
270 


350 
341 
346 


549 
479 
392 



The effects of texture have been investigated by a number 
of men, the work of von Seelhorst ^ and of Widtsoe ^ being 

^Montgomery, E. G., Water Requirements of Corn; Nebr. Agr. Exp. 
Sta., 25th Ann. Eep., p. xi, 1912. 

See also, Hellriegel^ H., Beitrdge zu den Naturwissenschaftliclien 
Grundlage des Acl'erbaus, Seite 629, Braunschweig, 1883. 

^Seelhorst, C, von., Uber den Wasserverbrauch von Boggen, Gerste, 
Weisen, und Kartoffeln ; Jour. f. Landwirtschaft, Band 54, Heft 4, 
Seite 316-342, 1906. 

^ Widtsoe, J. A., Irrigation Investigations. Factors Influencing Evapo- 
ration and Transportation ; Utah Agr. Exp. Sta., Bui. 105, 1909. 



WATER OF SOIL IN ITS RELATION TO PLANTS 193 

perhaps the most reliable. "While these investigators found 
in general that plants on heavy soils exhibited a low transpira- 
tion ratio, hasty conclusions must not be drawn. Since the 
fine-textured soils contain more nutrient materials, it is prob- 
able that this is also a factor. 

101. Amounts of water necessary to mature a crop. — 
Although it may be seen from the transpiration ratios cited 
that the amount of water necessary to mature the average 
crop is very large, a concrete example under humid condi- 
tions may be cited to advantage. A fair estimate of the dry 
matter produced in the above-ground parts of a forty-bushel 
crop of wheat would be about two tons. Assuming the tran- 
spiration ratio to be 300, the amount of water actually used 
by the plant would amount to 600 tons to the acre, or about 
5.2 inches of rainfall. This does not include the evaporation 
that is continually going on from the soil surface, which might 
very easily amount to as much more. The demand in total, 
to say nothing of run-off and drainage, is at least equal to 
10 inches of rainfall. 

102. Role of capillarity in supplying the plant with 
water. — A query arises at this point regarding the mode 
by which this immense quantity of water is supplied to the 
plant. The rootlets, especially their absorbing surfaces, are 
few in number as compared with the interstitial angles that 
contain most of the water retained in the soil. How, then, 
does the plant avail itself of water not in immediate contact 
with its rootlets? This question has been anticipated in the 
discussion concerning the capillary equilibrium which tends 
to occur in all soils. As soon as the rootlet begins to absorb 
at one point the film in that interstitial angle is thinned. 
A considerable convexity of the water surface occurs at that 
point, resulting in an inward pull, which causes the water to 
move in all directions toward that point. Thus a feeding 
rootlet by absorbing some of the moisture with which it is in 
contact, creates a condition of instability which results in 



194 NATURE AND PROPERTIES OF SOILS 

considerable film movement. It can, therefore, be said that 
capillarity is an important factor in any soil in supplying 
the plant with proper quantities of moisture. 

Many of the early investigators have over-estimated the 
distances through which this adjustment may be effective in 
properly supplying the plant. It must always be kept clearly 
in mind that it is the rate of water supply that is the con- 
trolling factor. Therefore, capillarity, although it may act 
through a distance of eight or ten feet if time enough be al- 
lowed, may actually be of immediate practical importance 
through only a few inches as far as the crop is concerned. No 
extended data are available as to this particular phase, but the 
knowledge of capillary movement indicates that capillarity of 
the soil is of greatest importance in a restricted zone immedi- 
ately around the surface of each absorbing root.^ 

103. Why plants wilt. — As has already been indicated, 
water may be of little use to a plant because of distance, since 
capillary action may not move the water rapidly enough 
for normal needs. Water near at hand may be unavailable 
through the obstruction of capillarity, friction in this case 
being the cause. As the rootlet thins the interstitial film at 
any point, the surface tension equilibrium is disturbed and 
water moves toward the absorbing surface. This movement is 
rapid enough foi plant needs until the film channels on the 
particles become thin. As such a condition approaches, fric- 
tion increases rapidly, cutting down the capillary movement 
to such an extent as to interfere with the normal functions 
of the plant. 

Wilting occurs, therefore, merely because the soil is unable 
to move the water rapidly enough for crop needs. As the 
friction increases very rapidly after the point of lento-capil- 
larity is reached, the wilting coefficient is a figure somewhat 

^Burr, W. W., The Storage and Use of Soil Moisture; Nebr. Agr. Exp. 
Sta., Ees. Bui. 5, 1914. 

Miller, E. C, Comparative Study of the Soot System and Leaf 
Areas of Corn and Sorghums; Jour, Agr. Ees., Vol. VI, No. 9, pp. 311- 
331, 1916. 



WATER OP SOIL IN ITS RELATION TO PLANTS 195 

less than the percentage representing the lento-capillarity. 
Since the inner capillary water moves very sluggishly if at 
all, wilting must occur before the plant has drawn to any great 
extent on this part of the capillary moisture. The hygroscopic 
water is, therefore, wholly unavailable to plants and generally 
some of the capillary as well, although Alway ^ has shown that 
under certain conditions the plant may reduce the moisture 
down to the hygroscopic coefficient. The ivilting coefficient ex- 
pressed in soil-moisture terms may be located somewhere be- 
tween the hygroscopic coefficient and the point of lento- 
capillarity. 

104. The wilting coefficient and its determination. — It 
has been known for many years that the common plants pos- 
sess different capacities for resisting drought. This has usu- 
ally been ascribed to one or more of three causes: (1) differ- 
ences in root extension; (2) differences in ability to become 
adjusted to a slow intake of water; and (3) differences in the 
osmotic pull that plants exert on the soil-water. The last two 
factors argue for different wilting coefficients for crops on the 
same soil. 

The extended work of Briggs and Shantz,- however, indi- 
cate that the permanent wilting point, expressed as a soil- 
moisture percentage, is practically the same for all plants. 
Later Caldwell ^ demonstrated that this relationship of the 
physical constants of the soil to the wilting point depends on 
the rate at which the plant loses water, showing that the soil 
factors are not entirely dominant in this respect. 

The conclusions of Briggs and Shantz, nevertheless, seem 

'Alway, F. J., Studies on the Eelation of the Non-available Water of 
the Soil to the Hygroscopic Coefficient ; Nebr. Agr. Exp. Sta., Res. Bui. 3, 
1913. 

" Briggs, L. J., and Sehantz, H. L. The Wilting Coefficient for Dif- 
ferent Plants and its Indirect Determination, U. S. Dept. Agr., Bur. 
Plant Ind., Bui. 280, 1912. 

^ Caldwell, J. S., The Eelation of Environmental Conditions to the 
Phenomena of Permanent Wilting in Plants; Physiological Researches, 
Station N, Baltimore; U. S. Dept. Agr.^ Vol. 1, No. 1, July, 1913. 



196 NATURE AND PROPERTIES OP SOILS 

more or less accurate for plants growing under humid condi- 
tions. If such is the case, it can be accounted for only by the 
fact that the soil forces in their effect on the wilting point 
are so powerful as to over-ride any distinguishing character- 
istics that the plant itself may possess, or at least reduce such 
influences within the error of actual experimentation. Crops 
wilt because they cannot get water fast enough, the wilting 
coefficient in a humid climate being the same for most plants 
growing on the same soil. 

Briggs and Shantz,^ in their investigations, devised a very 
satisfactory method for making determinations of the wilting 
point. Glass tumblers holding about 250 cubic centimeters 
of soil in an optimum condition were used. The seeds were 
placed in this soil after which soft paraffin was poured over 
the surface in order to stop evaporation, thus removing this 
disturbing factor in the capillary equilibrium of the moisture. 
The seedlings on germination were able to push through this 
paraffin. While the plants were developing, the tumblers 
were kept standing in a constant-temperature vat of water 
in order to prevent condensation of moisture on the inside 
of the glass. The vegetative room was under temperature 
control. When definite wilting occurred, as determined in 
a saturated atmosphere, a moisture determination was made 
on the soil. The resulting figure, expressed as percentage 
of moisture based on dry soil, represents the wilting coefficient 
for the soil used.^ 

It is evident that the wilting coefficient will be influenced 

^ Briggs, L. J., and Schantz, H. L., The Wilting Coefficient for Differ- 
ent Plants and its Indirect Determination; U. S. Dept. Agr., Bur. Plant 
Ind., Bui. 230, pp. 26-33, 1912. 

^ Bouyoucos classifies the capillary water into two groups, Free (the 
more active), and Capillary -absorbed (inner capillary). The distinction 
is made on the basis of his dilatometer (see foot-note, page 155) results, 
the portion which freezes at about 0°C being considered the more 
active. The point so established by his dilatometer gives in a general 
way the wilting coefSficient as defined by Briggs and Shantz. 

Bouyoucos, G. J., A New Classification of the Soil Moisture; Soil Sci., 
Vol. XI, No. 1, pp. 33-47, Jan., 1921. 



WATER OF SOIL IN ITS RELATION TO PLANTS 197 

by a number of soil conditions. Important among these is 
texture, which in itself really represents a group of soil con- 
ditions. In general the wilting point is much higher on a 
fine soil than one of a coarse nature. The following data from 
Briggs and Shantz ^ is interesting in this regard. The wilt- 
ing coefficient is shown to lie much nearer the hygroscopic 
coefficient than to the figure representing the maximum ab- 
sorption capacity as determined by the Hilgard method. 

Table XXXVII 

RELATION OF THE WILTING COEFFICIENT TO THE TEXTURE OF THE 

SOIL, THE HYGROSCOPIC COEFFICIENT AND THE CALCULATED 

MAXIMUM ABSORPTIVE CAPACITY OF THE SOIL 

FOR WATER. 



SOHi 


Hygroscopic 
Coefficient 


Wilting Point 


Calculated 
Maximum 

Absorption 
Capacity 


Coarse sand 

Fine sand 


.5 
1.5 
2.3 
3.5 
4.4 
6.5 
7.8 
9.8 
11.4 


.9 
2.6 
3.3 

4.8 

6.3 

9.7 

10.3 

13.9 

16.3 


25.7 

28.5 


Fine sand 


30.5 


Sandy loam ....... 

Sandy loam 

Fine sandy loam . . 
Loam 


34.9 
39.2 
49,1 
50.8 


Loam 


61.3 


Clay loam 


6S.2 



In studying the correlation of this wilting coefficient to 
soil conditions Briggs and Shantz - advanced the following 
relationships. Expressed as formulae, they represent methods 

^ Briggs, L. J., and Schantz, H. L., The Wilting Coefficient for Dif- 
ferent Plants and its Indirect Determination ; U. S. Dept. Agr., Bur. 
Plant Ind., Bui 230, p. 65, 1912. 

See also Heinrich, R., Uber das Vermogen der Pflanzen den Bodenen 
Wasser zu erscJiopfen; Jahresbericht der Agr.-chem., Band 18, Selte 368- 
372, 1875. 

^Briggs, L. J., and Shantz, H. L., The Wilting Coefficient for Dif- 



198 NATURE AND PROPERTIES OF SOILS 

of at least approximating the wilting point from other soil 
factors. These formulae ^ are arranged in the order of their re- 
liability, based on the data obtained by the authors: 

^ ^^., . ,„ . Moisture equivalent 

1. W iltmg coerncient = ^-^r 

o W14.- oi • ^ Hygroscopic coefficient 

2. Wilting coerncient = • ^ 

Water-holding capacity — 21 
o wi^- m • 4- (Hilg-ard Method) 

3. Wilting coerncient = — ■ — ^^^j 

While such formulae are only approximate in their applica- 
tion, they are valuable for rough calculations. They also show 
in a general way the correlations between the various moisture 
conditions established by experimental methods. 

105. The availability of the soil-water. — Prom the dis- 
cussions already presented regarding the forms of water in 
the soil, the ways in which they are held, and their movements, 
it is evident that all moisture present in a soil is not available 
for plant growth. Three divisions of the soil-water may be 
made on this basis: unavailable, available, and superfluous. 

It is obvious that all of the moisture below the wilting point 
is out of reach of the plant and may be classified as unavail- 
able. It includes all of the hygroscopic and that part of the 
capillary which is tightly held, the so-called inner capillary 
water. The amount of the capillary moisture unavailable to 
plants is much greater with clayey than with sandy soils. For 
example, a sand with a hygroscopic coefficient of 1.5 per cent. 

ferent Plants and its Indirect Determination; U. S. Dept. Agr., Bur. 
Plant Ind., Bui. 230, pp. 56-77, 1912. 

See also, Loughridge, R. H., Investigations in Soil Physics; Calif. Agr. 
Exp. Sta., Rep. 1892-3-4, pp. 70-100, 1894. Alway, F. J., and Clarke, 
V. L., Use of Two Indirect Metlwds for the Determination of the 
Hygroscopic Coefficient of Soils; Jour. Agr. Res., Vol. VII, No. 8, pp. 
345-359, Nov., 1916. 

^ Note that the wilting coefficient, moisture equivalent, water-holding 
capacity and hygroscopic coefficient are expressed in percentage of 
water based on dry soil. 



WATER OF SOIL IN ITS RELATION TO PLANTS 199 

and a wilting coefficient of 2.6 per cent, has 1.1 per cent, of 
water of a capillary nature unavailable. A clay loam having 
a hygroscopic coefficient of 11.4 per cent, and a wilting coeffi- 
cient of 16.3 per cent, would contain 4.9 per cent, of capillary 
water unavailable to crops. It must be remembered, however, 
that under certain conditions plants may reduce the capillary 
moisture almost to the hygroscopic coefficient.^ The moisture 
so obtained is probably not utilized for growth activities. 

Advancing from the wilting, or critical, moisture content of 
a soil, all the remaining capillary water is found to be avail- 

HYGRO. WILTING , LENTO- MAX. FIELD 

COEFF. X (^OINT TCAPILLARlTr CAPACITY 

^ ^ V OPTIMUM WATER ZONE /t/ 

HYG ROS — ' CAPILLARY WATER » <0RAVITAT10NAL 

COPIC water' I WATER 

V VJ J , 

>> y Yi y "^1 Y ' 

UNAVA1LABLE\ available SUPERFLUOUS 

AVAILABLE UNDER 
CERTAIN CONDITIONS 

Fig. 35. — Diagram showing the various forms of water that may be 
present in the soil and their relations to higher plants. 

able for normal plant use. However, when free water begins 
to appear, a condition detrimental to growth is established, 
conditions becoming more adverse as the saturation point is 
approached. This free water is designated as the superfluous 
water and its presence generates conditions unfavorable to 
plants. The bad effects of free water on the plant arise 
largely from the poor aeration that results from its presence.^ 
Not only are the roots deprived of their oxygen, but toxic 
materials tend to accumulate. Favorable bacterial activities, 
such as the production of ammonia and nitrates, are much re- 

* Alway, F. J., Studies on the Eelation of the Non-available Water 
of the Soil to the Hygroscopic Coefficient ; Nebr. Agr. Exp. Sta., Res. 
BuL 3, 1913. 

' It must be kept in mind that in a clayey soil the superfluous water 
may include some of the upper capillary moisture. 



200 NATURE AND PROPERTIES OF SOILS 

tarded also. The various forms of water in the soil and their 
availability to the plant are illustrated diagrammatically in 
Fig. 35, page 199. 

This diagram may be evaluated in a general way as below, 
using the sandy and clayey soils for which full physical data 
have already been given in Chapter VIII. (See footnote on 
page 179.) 

Table XXXVIII 

THE EVALUATION OF FIG. 35 FOB A SANDY AND CLAYEY SOIL, 
RESPECTIVELY. 



Hygroscopic coefficient , 

Wilting point 

Maximum field capacity 

Unavailable water 

Available water 

Superfluous water 



Sandy Soil 


Clayey Soil 


1.00 


10.00 


1.47 


14.70 


17.00 


44.00 


1.47 


14.70 


15.53 


29.30 


8.00 


1.60 



106. Optimum moisture for plant growth. — It is very 
evident that there must be some moisture condition of a soil 
which is best for plant development. This is usually desig- 
nated as the optimum content. It is not to be assumed, how- 
ever, that the total range of the available soil-water repre- 
sents this condition. Nor is this optimum water content in 
any particular soil to be designated by a definite percentage. 
In reality the moisture in a soil may undergo considerable 
fluctuation and yet allow the plant to develop normally.^ This 
ie because the physical condition of the soil changes with 
varying water content and the plant is able to accommodate 

*Wollny, E., Untersuchung iiber den Einfiuss der Wachsthumsfaktoren 
auf des Produktionsvermoqen der Kulturj)flanzen ; Forsch. a. d. Gebiete 
d. Agri.-Physik., Band 20,'Seite 53-109, 1897. 

Mayer, A., fiber den Einfiuss Jcleinerer oder grosser er Mangen von 
Wasser auf die EntwicTcelung einiger Kulturpflanzen ; Jour. f. Landw., 
Band 46, Seite 167-184, 1898. 



WATER OF SOIL IN ITS RELATION TO PLANTS 201 

itself to such a fluctuation without a disturbance in its normal 
development. Granulation has considerable influence on the 
range of optimum moisture conditions, since the better the 
granulation, the better able is the soil to accommodate itself 
to changes in water content without a disturbance of normal 
growth. In moisture conservation-^and control, a granular 
soil is one of the first improvements to be aimed at. Drainage, 
liming, addition of organic matter, and tillage, by leading up 
to such a condition, increase the effectiveness and economy of 
soil moisture utilization. 

Many of the ordinary farming operations have to do with 
the maintenance of an optimum moisture condition in the soil. 
During periods of excessive rainfall, especially during the 
growing season, conditions should be such as to allow the pres- 
ence of free water in the soil for the briefest time possible. 
This means adequate under-drainage and satisfactory arrange- 
ments whereby the run-off may be removed with but little 
damage. Moisture control also demands conservation meth- 
ods of more or less intensity in arid and semi-arid regions sup- 
plemented by irrigation, whereby the soil-moisture may never 
drop much below the point of lento-capillarity. By such ar- 
rangments the optimum moisture conditions, so essential to 
normal and uninterrupted crop growth, are maintained. 



CHAPTER X 
TEE CONTROL OF SOIL-MOISTUBE 

In the discussion of the water requirements of plants it 
was apparent that for a normal yield of any crop, the amount 
used by the plant alone was very great, varying from five to 
ten acre-inches according to conditions. Were this the only 
loss of water, the question of raising crops with given amounts 
of rainfall would be a simple one. Three further sources of 
water loss, however, are usually operating in the soil and tend- 
ing to lower the water that would go toward transpiration, a 
loss absolutely necessary for proper growth. The various 
ways by which water finds an exit from a soil are : (1) tran- 
spiration, (2) run-off over the surface, (3) percolation, and 
(4) evaporation. The diagram (Fig. 36) makes clear their 
relationships. 

It is immediately obvious that, as the losses by run-off, 
leaching, and evaporation increase, the amount of water left 
for crop utilization decreases. Some control of soil-water 
is, therefore, necessary both in an arid and a humid region. 
Under arid and semi-arid conditions, where run-off and per- 
colation are not of such great importance except where irriga- 
tion is practiced, loss by evaporation is of especial consequence, 
as it competes directly with the plant. Under humid condi- 
tions, losses by percolation and run-off seem to merit the 
greater attention, because of the loss of nutrients with the 
former and the erosion damage from the latter. The influence 
of evaporation, however, is not to be under-estimated or ne- 
glected. Control of moisture is, therefore, necessary in all 
regions. This control consists in so adjusting run-off, leach- 

202 



THE CONTROL OF SOIL-MOISTURE 



203 



mg, and evaporation as to maintain optimum moisture condi- 
tions in the soil at all times. Such control should result in 
a proper and economical utilization of soil-water by the plant. 
107. Run-off losses. — In regions of heavy rainfall or 
in areas where the land is sloping or rather impervious to 
water, a considerable amount of moisture received as rain is 
likely to be lost by running away over the surface. Under 



TR(C^NSP/RflT/ON. 




EVAPORATION. 






>V/ 



? / 




Fig. 36. — Diagram illustrating the various ways by which water may be 
lost from a soil. 



such conditions two considerations are important: (1) the loss 
of water that might otherwise be of use to plants; and (2) the 
erosion that usually occurs when much water escapes in this 
manner. Of the two, the latter is generally the more impor- 
tant. The amount of run-off varies with the rainfall and its 
distribution, the slope, the character of the soil, and the vege- 
tative covering. In some regions loss by run-off may rise as 
high as 50 per cent, of the rainfall, while in arid sections it 
is of course very low, unless the rainfall is of the torrential 
type as in the arid Southwest. 



204 NATURE AND PROPERTIES OF SOILS 

The quantity of water entering a soil is determined almost 
entirely by the physical condition of the soil. If it is loose 
and open, the water enters readily and little is lost over the 
surface as run-ofif. If, on the other hand, the soil is com- 
pact, impervious and hard, most of the rainfall runs away, 
and not only is there a serious loss of water, but considerable 
erosion may also result. The first step in checking run-off 
losses, therefore, is strictly physical in nature. Good tillage 
and plenty of organic matter by encouraging granulation have 
much to do with the proper entrance of water into the soil as 
well as with its economic utilization therein. 

108. Erosion by water and its control.^ — While every 
one is familiar with the importance of water in the forma- 
tion of alluvial and marine soils, the concurrent destructive 
action that is going on in the uplands is generally overlooked. 
This is due to the fact that erosion is often considered as more 
or less uncontrollable, an ill that can not be avoided. In 
"Wisconsin, for example, 50 per cent, of the tillable land is 
subject to erosion of economic importance.^ Even in as level a 
state as Illinois, 17 per cent, of the area is detrimentally 
eroded.^ The waste by erosion is as great in other states, 
even those of an arid climate. Davis * has estimated that 870 
million tons of suspended material are carried each year into 
the ocean by the streams of the United States. Since this is 
only a very small fraction of the soil brought down from the 

* Davis, K. O. E., Economic Waste from Soil Erosion; U. S. Dept. 
Agr., Year Book for 1913, pp. 207-220. 

Eamser, C. E., Terracing Farm Lands; U. S. Dept. Agr., Farmers' Bui. 
997, 1918. 

Eastman, E. E., and Glass, J. S., Soil Erosion in Iowa; la. Agr. Exp. 
Sta., Bui. 183, Jan., 1919. 

Fisher, M. L., The Washed Lands of Indiana; Ind. Agr. Exp. Sta., 
Circ. 90, Feb., 1919. 

^Wliitson, A. R., and Dunnewald, T. J., Keep Our Hillsides from 
Washing; Wis. Agr. Exp. Sta., Bui. 272, Aug., 1916. 

* Hosier, J. G., and Gustaf son, A. F., Soil Physics and Management, 
p. 358, Philadelphia, 1917. 

••Davis, E. O. E., Economic Waste from Soil Erosion; U. S. Dept. Agr., 
Year Book for 1913, p. 213, 



THE CONTROL OF SOIL-MOISTURE 205 

uplands by running water, erosion is no insignificant factor 
in soil management considerations. 

Two types of erosion are generally recognized, sheet and 
gully. In the former, soil is removed more or less uniformly 
from every part of the slope. Gullying occurs where the vol- 
ume of water is concentrated, resulting in the formation of 
ravines by undermining and downward cutting. Both types 
of erosion are serious. 

A number of different methods for the effective prevention 
and control of erosion may be utilized. Anything that will 
increase the absorptive capacity of the soil, such as deep plow- 
ing, surface tillage, and increase of organic matter, will lessen 
the run-off over the surface. On steep slopes, however, such 
influence is of little importance, since during heavy rainfall 
absorption is too slow to lessen materially the surface losses. 
In cultivating corn and similar crops, it is important that the 
last cultivation be across the slope rather than with it. On 
long slopes subject to erosion, the fields may be laid out in long 
narrow strips across the incline, alternating the tilled crops, 
such as corn and potatoes, with hay and grain. The grassed 
areas tend to check the surface flow of water. Where the 
slopes are subject to very serious erosion, they should either be 
reforested or kept in permanent pasture, guarding always 
against incipient gullying. 

About the only effective means of controlling sheet erosion 
is by terracing of some kind. Strong prejudice exists in many 
communities against terraces, since they usually waste land, 
are often unsightly and are a serious obstacle to harvesting 
machinery. The Mangum terrace ^ however, is worthy of es- 
pecial attention, since it obviates the really serious objections 
to the ordinary terrace while maintaining the desired water 
control. The Mangum terrace is generally a broad bank 
of earth with gently sloping sides, contouring the field at a 

* First constructed by P. H. Mangum of Wake County, North Caro- 
lina. 



206 NATURE AND PROPERTIES OF SOILS 

grade from 10 to 12 inches to the 100 feet. It is usually 
formed by back-furrowing and scraping. The interval be- 
tween the embankment depends on the slope. Since the terrace 
is low and broad, it may be cropped without difficulty and 
offers no obstacle to cultivating and harvesting machinery. 
It wastes no land, and eliminates breeding places for insects. 

Small gullies, while at first insignificant, soon enlarge into 
deep unsightly ravines. While they may be plowed-in or 
otherwise filled up, such a procedure is generally a waste of 
time, since the gullies form again with the next heavy wash. 
A number of different methods are in use for the control of 
gullying, depending on conditions. Staking is a very common 
procedure, the size of the stakes increasing with the magni- 
tude of the gully. The stakes are usually interwoven with 
brush, although stone, straw, and other material may be 
utilized. If brush or other loose material is used, it should 
be staked to the ground or held down by stone or dirt. Other- 
wise, the water will run beneath the fill and no benefit will 
result. Dams of earth, concrete, or stone are often installed 
with success. They must be supplemented by a tile-drain 
outlet, however, with an elbow just above the dam. The dam 
checks the water until it rises to the level of the elbow outlet 
and is then carried away through the tile. Most of the sedi- 
ment is deposited above the dam and the gully is slowly filled. 

109. Percolation losses and their control. — When at 
any time the amount of rainfall entering a soil becomes greater 
than its water-holding capacity, losses by percolation will 
result. The losses will depend largely on the amount and 
distribution of the rainfall and the capability of the soil to 
hold moisture. The objectionable features of excessive per- 
colation are two: (1) the actual loss of water, and (2) the 
leaching-out of salts that may function as nutrients to plants. 

The results from the Rothamsted lysimeter ^ from 1871- 

* Hall, A. D., The Bool^ of the RotJiamsted Experimejits, p. 22, New 
York, 1917. 



THE CONTROL OF SOIL-MOISTURE 



207 



1913 on a bare clay loam three feet deep are interesting as to 
the light they afford regarding actual drainage losses in humid 
regions : 

Table XXXIX 

PERCOLATION THROUGH A SIXTY-INCH COLUMN OF BARE CLAY 

LOAM. ROTHAMSTED EXPERIMENT STATION, ANNUAL 

AVERAGE OF 42 YEARS. 



Periods 


EAINFAIjL 

Inches 


Drainage 
Inches 


Percentage 
OF Eainfall 
AS Drainage 


Dec.-Feb 

Mar.-May 

June-Aug 


6.77 
5.96 
7.83 
8.29 


5.58 
2.11 
1.82 
4.50 


82.4 
35.4 
23.2 


Sept.-Nov 


54.2 






Mean Total 


28.85 


14.01 


48.8 



It appears from these figures that the drainage loss is much 
lower in summer than winter, the ratio being about one to 
three. It is also to be noted that about 50 per cent, of the 
rainfall in such a climate as England is lost by percolation 
through a bare soil. This compares fairly well with Wollny's ^ 
summary on eighteen soils in England, Switzerland, and Ger- 
many. These soils, most of which were bare, f^howed a loss 
of over 41 per cent, of the rainfall by drainage. 

Recent results,- due to variable conditions, are by no means 
in agreement, ranging from a low to a very high percentage 
loss of the rainfall. It seems fair to assume, however, that, 
as soils are handled in humid regions, over half of the rain- 
fall is lost by percolation and run-off combined. 

Percolation seems to be influenced, not only by the amount 

* Wollny, E., Untersuchungen uber die Sickerwassermengen in verscMe- 
denen Bodenarten; Forsch. a. d. Gebiete d. Agri.-Physik., Band 11, 
Seite 1-68, 1888. 

' For excellent review of literature see Lyon, T. L., and Bizzell, 
J. A., Lysimeter Experiments ; Cornell Agr. Exp. Sta., Memoir 12, June, 
1918. 



208 NATURE AND PROPERTIES OF SOILS 

of rainfall and its distribution, but also by evaporation, the 
character of the soil, and the presence of a crop. As the rain- 
fall increases, percolation increases, being much greater in 
New York, for example, than in Utah. Evaporation has a 
marked influence, reducing drainage losses to a considerable 
degree. The drainage through sandy soils is generally larger 
than through clayey soils under strictly humid conditions and 
where run-off is a factor. When evaporation is high, sandy 
soils have been known to percolate very much less than those 
of a heavier nature.^ Field crops, in that they utilize a large 
amount of moisture, have always been found to reduce per- 
colation losses. 

The loss of moisture by percolation is the least objectionable 
feature of the phenomenon, since it is often necessary, espe- 
cially during the spring and summer, to rid the soil very 
quickly of superfluous water. The loss of nutrient salts is 
more vital, since the materials so carried away might be used 
by plants. The loss of nitrogen, calcium, and potassium from 
a bare clay loam at Cornell University ^ over a period of ten 
years averaged, respectively, 69, 398, and 72 pounds an acre 
annually. This is equivalent to an acre loss of 419 pounds 
of sodium nitrate, 995 pounds of calcium carbonate and 137 
pounds of potassium chloride every year, which is a larger 
amount of nutrient material than is removed by an average 
crop. 

Control of percolation is exerted, not so much to save water, 
as to conserve nutrients. As water enters a soil it moves 
downward and is continually changing into the capillary state. 
If the absorptive capacity of the soil is high, little of the rain- 
fall may appear as drainage. The presence of organic matter 
and the influence of good tillage will do much toward check- 
ing drainage losses. Once the absorptive capacity of the soil 

* Fraps, G. S., Losses of Moisture and Plant Food by Percolation; Tex. 
Agr. Exp. Sta., Bui. 171, 1914. 

* Unpublished data. Cornell Agr. Exp. Sta., Ithaca, N. Y. 



THE CONTROL OP SOIL-MOISTURE 



209 



is reached, however, the drainage should be as rapid and com- 
plete as possible in order to insure good sanitation. The main- 
tenance of a high absorptive capacity for available water and 
the facilitation of rapid drainage are the secrets of rational 
percolation control. 




Fig. 37. — Influence of drainage on the ground water and the extent of 
the root zone. 

In this connection it is well to remember that drainage losses 
are profoundly affected by cropping. The following data from 
the Cornell Experiment Station are especially interesting in 
this regard. The data for the Dunkirk and Volusia soils are 
for ten and fifteen years respectively: 

Table XL 

AVERAGE ANNUAL LOSS OP WATER BY PERCOLATION FROM BARE 
AND CROPPED SOILS. CORNELL LYSIMETER TANKS. 



Conditions 


Eainfall 
Inches 


Percolation 
Inches 


Eainfall as 

Percentage op 

Drainage 


Dunkirk clay loam : 
Bare 


32.41 
32.41 

32.97 
32.97 


24.92 

18.70 

27.13 
20.62 


76.8 


Cropped 


57.7 


Volusia silt loam: 
Bare 


82.3 


Cropped 


62.5 



210 



NATURE AND PROPERTIES OF SOILS 



Table XLI 

average annual loss of nutrients by percolation from 
bare and cropped soils. cornell lysimeter tanks. 



Conditions 


Annual Loss in Pounds an Acee 




NITROGEN 


CALCIUM 


POTASSIUM 


Dunkirk clay loam : 
Bare 


69.0 
7.3 
2.5 

51.8 
10.2 


397.9 
247.1 
259.9 

341.4 
356.4 


72.0 


Rotation 

Grass 

Volusia silt loam: 
Bare 


57.3 
61.7 

84.5 


Cropped 


73.2 



The influence of the crop on percolation is obvious, the loss 
of water by drainage being markedly decreased. The 
saving of nutrient is also very marked, especially as regards 
the nitrogen. The loss of nitrogen is only about one-seventh 
as much from the soils under a rotation, as where the land 
was bare, while the saving of calcium and potassium is con- 
siderable. The importance of catch- and cover-crops in eco- 
nomical soil management need not be emphasized further. 

110. Drainage.^ — While percolation, especially in hu- 
mid regions, causes the loss of a large proportion of the 
rainfall received and carries away in addition many tons of 

^Klippart, J. H., Principles and Practice of Land Drainage; Cin- 
cinnati, 1894. 

Miles, M., Land Drainage; New York, 1897, 

Faure, L., Drainage et Assainissement Agricole des Terres; Paris, 
1903. 

Elliott, C. G., Drainage of Farm Lands; U. S. Dept. Agr., Farmers' 
Bui. 187, 1904. 

King, F. H., Irrigation and Drainage, Revised Edition; Part IT, New 
York, 1909. ' 

Warren, G. M., Tidal Marshes and their Beclamation; U. S. Dept. 
Agr., Office Exp. Sta., Bui. 240, 1911. 

Woodward, S. M., Land Drainage by Means of Pumps; U. S. Dept. 
Agr., Office Exp. Sta., Bui. 243, 1911. 

Elliott, C. G., Engineering for Land Drainage; New Yorkj 1912. 

Parsons, J. L., Land Drainage; Chicago, 1915. 



THE CONTROL OF SOIL-MOISTURE 211 

soluble material, it is generally wise to facilitate the rapidity 
of its action while checking, if possible, its magnitude. The 
encouragement of the rate of percolate is spoken of as land 
drainage, which is the process of removing the excess or 
superfluous water from the soil as rapidly as possible. 
Excess water, by interfering with aeration, sets up unsanitary 
conditions within the soil. By draining the land many favor- 
able reactions are promoted. Granulation is encouraged, 
heaving is checked, while the root zone and water capacity 
of the soil are markedly increased. By facilitating aeration, 
favorable chemical and biological changes are encouraged, 
thus increasing the nutrients available for plants. The sum- 
total of good drainage is an increase of crop production to 
such an extent as to meet the investment costs and pay a hand- 
some profit besides. 

While the drainage of swamps and the reclamation of over- 
flow areas are urgent, the drainage of lands already under 
crop is more important. Practical farm drainage is para- 
mount in almost every community, even in arid regions where 
irrigation must be practiced. Tw^o types of drainage are 
feasible — open and closed. Ditch drainage is the usual type 
of the first group. Ditches have the advantage of large ca- 
pacity and are able to carry water at a low grade. On the 
other hand, they waste land, are ineffective and inconvenient, 
encourage erosion and demand a yearly up-keep expenditure. 
Wherever possible under-drains should be used. 

Jeffery, J. A., Text-Book, of Land Drainage; New York, 1916. 

Fippin, E. O., Drainage in Neiu York; Cornell Agr. Exp. Sta., Bui. 
254, 1908. 

Brown, C. F., Farm Drainage; Utah Agr. Exp. Sta., Bui. 123, 
1913. 

Lynde, H. M., Farm Drainage in North Carolina; N. C. Agr. Exp. 
Sta., Bui. 234, 191.5. 

Yarnell, D. L., Trenching Machinery Used for the Construction of 
Trenches for Tile Drains; U. S. Dept. Agr., Farmers' Bui. 698, 1915. 

Leidigh, A. H,, and Gee, E. C, Tile Drainage; Tex. Agr. Exp. Sta., 
Bui. 188, 1916. 

Hart, E. A., The Drainage of Irrigated Farms; V. S. Dept. Agr., 
Farmers' Bui. 805, 1917. 



212 NATURE AND PROPERTIES OF SOILS 

111. Tile drains are the only reliable means of under- 
drainage under all conditions. While stone drains ^ are 
of value in certain cases, they must always be short and 
are likely to clog. Besides, their drainage is slow and in- 
efficient. On silty soil they do not long remain in service. 
The operation of the tile drain is simple. The tile, generally 
about twelve inches long with a diameter varying with the 
water to be carried, are laid end to end in strings, on the 
bottom of a trench of sufficient slope, a carefully protected 
outlet being provided. The tile are then covered with earth, 
straw or surface soil often being placed directly around the 
tile to facilitate the entrance of the water. The superfluous 
water enters the tile through the joints, mostly from the 
sides. As a consequence, the tops of the joints may be cov- 
ered with paper, cloth or even cemented in order to prevent 
the entrance of silt or quick-sand. The function of a tile 
drain system is twofold: (1) to collect the superfluous water 
and (2) to discharge it quickly from the land. 

Where the land possesses considerable natural drainage, the 
tile are laid along the depressions. This is spoken of as -the 
natural system of drainage in that the tile facilitate the quick 
removal of the water from the places of natural accumulation. 
Where the land is level or gently rolling, it often needs uni- 
form drainage. A regular system must then be installed. 
This may be either of the fishbone or gridiron style, or a 
modification or combination of the two, natural drainage being 
taken advantage of where possible. Where springs or seep- 
age spots occur, cut-off systems must be devised. (See Figs. 
38 and 39.) 

'Stone drains are built by arranging stone in a properly located and 
graded trench in such a manner as to provide a continuous channel 
or throat from the upper end of the drain to the lower. One of the 
safest modes of construction from the standpoint of clogging is to place 
flat stone on edge in the trench with their faces parallel to the walls 
of the ditch. The spaces between the stone provide for the movement 
of the drainage water. 



THE CONTROL OF SOIL-MOISTURE 



213 



Every regular system consists of two parts, the laterals and 
the main drain. The laterals are usually constructed of 
three 3- or 4-inch tile, seldom smaller. These laterals should 
always enter the main at an angle of about 45 degrees. This 
causes a joining of the currents with no loss of impetus and 






Hfgh 

Ground ^^ 












\ 







Fig. 38. — Natural (1) and interception (2) systems for laying tile 
drains. 

allows the more rapidly moving lateral streams to speed up 
the flow in the main drain. The size of the main depends on 
the rainfall, the area drained, and the slope. It, of course, 
must be larger near the outlet than at any other point. The 
following practical table from Elliott ^ indicates the influence 



^Elliott, C. G., Engineering for Land Drainage; p. 108, New York, 
1912. 



214 



NATURE AND PROPERTIES OF SOILS 



of area and slope on the size of the main near the outlet of 
any system: 

Table XLI 

grades to a hundred feet in decimals of a foot with ap- 
proximate equivalents in inches, 





Grades to a Hundred Feet 


IN Decimals of a Foot with 


Diameter 




Approximate Equivalents in Inches 




OF Tile 














(in Inches) 


y-2 inch 


1 iuch 


2 inches 


3 inches 


6 inches 


9 inches 




0.04 


0.08 


0.16 


0.25 


0.50 


0.75 




Acres 


Acres 


Acres 


Acres 


Acres 


Acres 


5 


17.3 


19.1 


22.1 


25.1 


32.0 


37.7 


6 


27.3 


29.9 


34.8 


39.6 


50.5 


59.4 


7 


39.9 


44.1 


51.1 


58.0 


74.5 


87.1 


8 


55.7 


61.4 


71.2 


80.9 


103.3 


121.4 


9 


74.7 


82.2 


95.3 


108.4 


138.1 


162.6 


10 


96.9 


106.7 


123.9 


140.6 


179.2 


211.1 


12 


152.2 


167.7 


194.6 


221.1 


281.8 


331.8 



The grade necessary for the satisfactory operation of a tile 
drain system varies with the system itself and the portion 
under consideration. The grade of the main drain may be 
very low, especially if the laterals deliver their water with a 
high velocity. In general, the grade will vary from 4 to 20 
inches to the hundred feet, 8 inches being more or less ideal. 
The depth of the tiles beneath the surface and the distance 
between laterals will vary with the soil. With sandy soils 
the tile may be placed as deep as 3 or 4 feet. With clayey 
soils the depth must be shallower, ranging from 15 to 30 
inches, while the interval is reduced as the soil becomes finer 
in texture. On a clayey soil the distance between the strings 
is sometimes as low as 35 feet although 50 to 70 feet is com- 
moner. 

The maintenance cost of a tile drain system is low, the only 
especial attention needful being at the outlet. The outlet 



THE CONTROL OF SOIL-MOISTURE 



215 



should be well protected, so that the end tiles may not be 
loosened and the whole system endangered by clogging with 
sediment. It is well to embed the end tile in a masonry or 
concrete wall. The last eiglit or ten feet of tile may even be 
replaced by a galvanized iron pipe or with sewer tile, thus 



<J I 



M. 



-vl 



Fig. 39. — Gridiron and fishbone systems for laying tile drains. 



insuring against damage by frost. The water should flow 
freely from a tile drain system, as a drowned outlet inter- 
feres with efficient drainage. The opening of a tile drain sys- 
tem is usually protected by a gate or by wire in such a man- 
ner as to allow the water to flow out freely but preventing 
rodents from entering in dry weather. (See Fig. 40.) 

As with any other improvement, tile drainage must be made 



216 



NATURE AND PROPERTIES OF SOILS 



to pay. If rapid efficient drainage can not be assured at a 
reasonable cost and under such conditions that the increased 
crops will return a good profit on the investment, tile drains 
should not be installed. 

112. Evaporation losses. — Evaporation of soil-water takes 
place almost entirely at the surface, exceptions being 
where large cracks occur, which allow thermal loss directly 
from the subsoil. This loss of water by direct evaporation 
from the soil may be excessive and may result in direct reduc- 




FiG. 40. — Cement block at the outlet of a tile drain. 



tion of crop yield, a type of loss so familiar that examples 
hardly need be cited. In the results with the Rothamsted rain 
gauges (see page 207), about 50 per cent, of the annual rain- 
fall was regained in the drainage water. Since the gauges bore 
no crop, the remaining 50 per cent, must have been lost by 
evaporation. It should be noted that in the summer months 
under warm temperature, this loss was greatest, amounting 
to 75 per cent, of the rainfall. Correspondingly, in the semi- 
arid and arid sections of the country where there is little or 
no drainage, the rainfall is almost all lost by evaporation. 
Evaporation from land surface has an appreciable effect on 



THE CONTROL OF SOIL-MOISTURE 



217 



the amount of rainfall. Even in humid regions, where the 
annual rainfall is ample for maximum crop production, the 
yields are frequentlj^ reduced below the profit point by pro- 
longed periods of dry weather in the growing season during 
which the loss of water from the plants, coupled with the loss 
from the soil and through weeds, exhausts the moisture sup- 
ply very rapidly. 

While run-ofi" and percolation are directly proportional to 
the rainfall, loss by evaporation does not vary to such a de- 
gree. The loss by percolation depends almost directly on the 
amount of rainfall above the retentive power of the soil. In 
years of heavy precipitation losses by percolation increase. 
Evaporation from the soil depends largely on the length of 
time that the soil surface is moist, and this will not vary 
markedly from year to year. The following figures from the 
Rothamsted ^ sixty-inch drain gauge may be quoted in this 
regard : 

Table XLIII 

rainfall, drainage and evaporation at the rothamsted 
experiment station, 1871 to 1912. 



Conditions 


Eainfall 
Inches 


Percolation 
Inches 


Evaporation 
Inches 


Maximum rainfall, 1903. . . . 
Mean total for 42 years .... 
Minimum rainfall, 1898 . . . . 


38.69 

28.75 
20.49 


24.23 

13.93 

7.69 


14.46 
15.32 
12.80 



A rough calculation may be made which will show the ap- 
portionment of the yearly rainfall in a humid region of the 
temperate zone between the four forms of losses — run-off and 
percolation, evaporation, and transpiration. The percolation 
under a rainfall, say, of 28 inches, as shown by the Rotham- 



^Hall, A. D., The Book of the Bothamsted Experiments; p. 22, New 
York, 1917. 



218 NATURE AND PROPERTIES OF SOILS 

sted work, is roughly 14 inches. Run-off and percolation may 
be considered as about 50 per cent. The water requirement of 
an ordinary crop is about 7 inches. This leaves a loss of 7 
inches to be credited to evaporation. In other words, in a 
clay loam soil in a climate like that of England, one-half 
the rainfall goes as run-off and percolation, while the other 
half is divided about equally between the plant and loss by 
evaporation. While run-off and percolation may be checked 
to some extent, not enough conservation can occur in this di- 
rection to tide a crop over a period of drought. Some con- 
sideration should, therefore, be directed towards the check- 
ing of loss by evaporation, since moisture thus saved means 
just that amount added to the water available for the use of 
the crop growing on the soil. 

113. Evaporation control. — Any material applied to the 
surface of a soil primarily to prevent loss by evaporation or to 
keep down weeds may be designated as a mulch. Mulches are 
of two general sorts, artificial and natural. In the former case, 
foreign material is merely spread over the soil surface. Man- 
ure, straw, leaves, and the like may be used successfully. 
Such mulches while effective, especially in preventing weed 
growth, are not generally applicable to field crops where in- 
ter-tillage is practiced, since they would make cultivation im- 
possible. Their use is, therefore, limited to such crops as 
strawberries, blackberries, and the like. 

The second type of mulch is called a soil-mulch since it is 
formed from soil itself. With proper tillage, a loose dry layer 
of soil may be formed on the surface. Such a layer is designed 
to obstruct capillary movement to such an extent as to reduce 
evaporation loss to a minimum. In. theory a soil-mulch should 
be formed as quickly as possible so that the only moisture 
sacrificed will be that which is present in the soil forming 
the mulch. Moreover, the mulch should be renewed after 
every rain and should, except in special cases, be not more 



THE CONTROL OF SOIL-MOISTURE 219 

than tliree inches deep. Late in the season, especially for 
coi^n, the cultivation should be shallow to prevent root-prun- 
ing.' 

For many years cultivation for a soil-mulch has been ad- 
vocated for two reasons: (1 ) checking of evaporation, and (2) 
the killing of weeds. Either procedure, if successful, will 
allow the crop a larger proportion of the rainfall. Recent 
experimental results, however, seem to indicate that a soil- 
mulch with an intertilled crop does not check evaporation 
compared with a soil uncultivated and kept free of weeds. 
This is probably due to the fact, that even vsdth moisture 
a limiting factor, the water sacrificed in renewing the mulch 
is not offset by that conserved. The tendency of soils, espe- 
cially those of a sandy character to self-mulch as well as the 
action of the roots of the crop in intercepting the water, may 
also be factors. Under greenhouse conditions and in regions 
of very little rainfall, the soil-mulch probably does conserve 

* Since a great many of the inter-tilled crops are shallow-rooted, 
great care should be exercised in cultivation, especially toward the latter 
part of the growing season. Corn and fptatoes are especially influenced 
by root-pruning. The following data ^ averaged for 7 years are 
pertinent: 

Influence of Eggt-Pruning on the Yield of Corn in Bushels to 

THE Acre. Average gp 7 Years, University 

GF Illinois 



Treatment 



Yield 



No cultivation, weeds kept down with hoe. 

Shallow cultivation 

Deep cultivation 



Shallow cultivation, roots unpruned 

Shallow cultivation, roots pruned with knife. 

Surface scraped, roots unpruned 

Surface scraped, roots pruned with knife. . . . 



67.7 
70.8 
68.6 

74.8 
61.6 

80.7 
68.3 



^ Mosier, J. G., and Gustafson, A. F., Soil Moisture and Tillage for 
Corn; 111. Agr. Exp. Sta., Bui. 181, 1915. 



220 



NATURE AND PROPERTIES OF SOILS 



moisture. The following figures ^ are representative of the 
data available regarding these points : 

Table XLIV 

moisture content op bare irrigated and dry-land plots, 

treated in various ways, expressed in total inches of 

water in upper 6 feet of soil. garden city, 

KANSAS, 1914. 





Irrigated 


Dry Land 


Treatment 


MAR. 30 


SEPT. 16 


GAIN OR 
LOSS 


MAR. 30 


SEPT. 16 


GAIN OR 
LOSS 


6-inch mulch. . . . 

3-inch mulch 

Bare surface 

Weeds 


17.6 
18.1 
17.8 
16.4 


15.9 

16.6 

15.6 

9.1 


—1.7 
—1.5 

—2.2 
—7.3 


11.8 
11.3 
11.5 

10.8 


12.4 

ia.7 

12.0 

8.0 


+ .6 
+ .4 
+ -5 
—2.8 



Table XLV 

effects of various methods of tillage on the yield of corn 

and the average percentage of moisture in the soil 

to a depth op 40 inches. average op 8 years ' 

test at the university of illinois.^ 

mean rainfall, 33.7 inches. 



Treatment 


Yield op Corn 
Bushels 
Per Acre 


Average 
Percentage 
OF Moisture 

IN Soil 


Not plowed or cultivated : 

Kept bare of weeds only. . . . 
Plowed and seedbed prepared : 

Kept bare of weeds only 

Weeds allowed to grow 

Three shallow cultivations .... 


31.4 

45.9 

7.3 

39.2 


23.1 

22.3 

21.8 
21.9 



^Call, L. E., and Sewell, M. C, The Soil Mulch; Jour. Amer. Soe, 
Agron., Vol. 9, No. 2, pp. 49-61, Feb., 1917. 

-Hosier, J. G., and Gnstnfson, A. F., Soil Moisture and Tillage for 
Corn; 111. Agr. Exp. Sta., Bui. 181, Apr., 1915. 



THE CONTROL OF SOIL-MOISTURE 221 

The above data, which are amply corroborated by other 
investigations,^ indicate that, witli an uncropped light silt 
loam in a semi-arid region, the soil-mulch is of little practical 
importance in conserving moisture. Moreover, the results in 
Illinois as well as Kansas are no better on cropped land, the 
cultivation seemingly having little influence on either mois- 
ture content or crop yield. The importance of a good seed- 
bed is very strikingly shown by the Illinois data, as is also the 
necessity of weed control. The weeds not only appropriate 
moisture that should go to the crop, but at the same time 
absorb nutrients that should be utilized in other ways. 

Certain general conclusions are unavoidable in respect to 
a soil-mulch.- In the first place, a cropped cultivated soil 
seems no more effective in preventing evaporation than one 
that is cropped and uncultivated. Whether this extends to 
bare soil under all conditions has not been conclusively shown. 
In the second place, the elimination of weeds seems to be the 
most important benefit of cultivation. It must be remem- 
bered, however, that cultivation may exert some benefit on 
aeration of a heavy soil and certainly encourages granulation 
to a certain extent. 

114. Summary of moisture control. — Moisture control 
seems to fall logically under three heads: (1) run-off, (2) 
drainage, and (3) evaporation. The detrimental influence of 
run-off over the surface is due to erosion,, the loss of the water 

* Young, H. J., The Soil Mulch; Nebr. Agr. Exp. Sta., 25th Ann. 
Eep., pp. 124-128, 1912. 

Barker, P. B., The Moisture Content of Field Soils Under Different 
Treatments; Nebr. Agr. Exp. Sta., 25th Ann. Eep., pp. 106-110, 1912". 

Gates, J. S., and Cox, H. R., The Weed Factor in the Cultivation of 
Corn; U. S. Dept. Agr., Bur. Plant Ind., Bui. 257, 1912. 

Alway, F. J., Studies on the Relation of the Non-available Water of 
the Soil to the Hygroscopic Coefficient ; Nebr. Agr. Exp. Sta., Res. Bui. 
3, 1913. 

Burr, W. W., The Storage and Use of Soil Moisture; Nebr. Agi-. Exp. 
Sta., Res. Bui. 5, 1914. 

^^See Call, L. E., and Sewell, M. C, The Soil Mulch; Jour. Amer. 
Soc. Agron., Vol. 9, No. 2, pp. 49-61, Feb., 1917, 



222 NATURE AND PROPERTIES OF SOILS 

itself being of minor importance. Similarly percolation loss 
is important because of the nutrients carried away, rather 
than because of the waste of the water. Since a certain 
amount of percolation must take place and because a water- 
logged soil is unsanitary for plants, rapid drainage is essen- 
tial. Of the various methods available, tile drainage is the 
most satisfactory. Evaporation loss, as with run-off and per- 
colation, can be but very slightly checked. The soil-mulch is 
important in that the cultivation necessary to produce it keeps 
down the weeds and in this manner it eliminates serious crop 
competition for nutrients and moisture. 



CHAPTER XI 
SOIL HEAT^ 

It is universally recognized that biological activity is an 
energy expression and that such activity will not continue 
unless certain temperature relations are maintained. With 
higher plants this heat relation has two phases, the tempera- 
ture of the air and that of the soil. The former is clearly 
a climatic factor and, except on a small scale, is beyond the 
control of man. The temperature of the soil, in a similar way, 
is subject to no radical regulation, yet soil management meth- 
ods provide means whereby certain small but biologically vital 
modifications can be made, climatically unimportant but prac- 
tically worthy of careful consideration. 

115. Importance of soil heat. — Normal plant growth is 
practically suspended at a temperature of 40° F., while the 
germination of most seeds does not take place even at this 
point. In general, it is poor practice to place certain seeds 
and plants in soil where growth activities will not occur at 
once, since bacteria and fungi, active at low temperatures, 
may sap their vitality and ultimately cause their destruction. 
Three groupings of higher plants may be made as far as their 
temperature relationships are concerned. Wheat represents 
the crops that germinate and grow at relatively low tempera- 
tures. Maize requires a medium temperature for proper 
growth, while pumpkins and melons typify crops, the heat 
requirements of which are very high. The following data 

^ For a bibliography of the literature of soil heat see Bouyoucos, 
G. J., An. Investigation of Soil Tevriperatwre and Some of the Most 
Important Factors Influencing It; Mich. Agr. Exp. Sta., Tech. Bui. 17, 
pp. 194-196; 1913. 

223 



224 



NATURE AND PROPERTIES OF SOILS 



from Haberlandt^ show the need of careful temperature con- 
trol in the propagation of plants: 

Table XL VI 

GERMINATION TEMPERATURES 



Crop 


Minimum 


Optimum 


Maximum 


Wheat 


40° F 

49 

52 


84° F 

93 

93 


108° F 


Maize 

Pumpkin 


115 
115 


Table XLVII 
growth temperatures 


Crop 


Minimum 


Optimum 


Maximum 


Wheat 


32-40° F 

40-51 

51-60 


77- 78° F 
88- 98 
98-111 


88- 98 


Maize 

Pumpkin 


98-111 
111-122 



Other desirable biological activities, especially those due to 
bacteria, are impeded if not brought entirely to a standstill by 
a temperature of 32° F. Such changes as decomposition of 
organic matter, the production of ammonia from nitrogenous 
organic matter, the formation of nitrate nitrogen from am- 
monia and the fixation of atmospheric nitrogen depend on 
heat conditions which, fortunately, are optimum for the de- 
velopment of higher plants. 

Desirable chemical reactions in the soil are much retarded 
by low temperatures, heat greatly accelerating such phe- 
nomena. This is especially noticeable in the tropics where 
weathering is much more rapid and intense than in temperate 
regions. Much of the hydration, oxidation, carbonation and 
solution in a temperate climate occurs in the summer when 
high temperature lends its aid to such desirable reactions. 

* Haberlandt, F., Bie Ob even und TJnteren Tempcraturgrense fiir die 
Keimung der Wichtigeren Landtvirthschaftlichen Sdmereien; Landw. 
Versuchs. Stat., Band 17, Seite 104-106, 1874. 



SOIL HEAT 225 

The effect of heat on the physical changes within the soil 
is often vital. The influence that temperature variation exerts 
on percolation, evaporation, and capillary movement of soil- 
water; on diffusion of gases, vapors, and salts in solution; 
and on osmosis, surface tension and vapor tension phenomena, 
may serve as examples of such heat modifications. Moreover, 
successive freezing and thawing of the soil greatly aids in 
granulation and aeration. The aspirating effect of a slight 
change in temperature is so tremendous as often markedly to 
renew the oxygen supply of the furrow slice. 

In order fully to understand the practical and scientific 
relationships involved in even a partial control of soil heat, 
a certain cycle of events must be recognized. The cycle be- 
gins with the acquisition of energy from the sun and the 
establishment of certain temperature relations which depend 
on absorption activity and the facility with which heat is 
transferred from place to place. The important chemical, 
]ihysical, and biological transformations within the soil de- 
pend as much on such movements as on the intensity of the 
temperature factors. Much of the energy so involved is soon 
lost from the soil, returning again to the space from which 
it came. Thus tlie cycle is completed, having provided the 
temperature conditions necessary for successful crop produc- 
tion. (See Fig. 41.) 

116. Insolation received by the soil. — The sun supplies 
practically all of the energy by means of which the soil main- 
tains a temperature suitable for its normal activities. Energy 
from other sources is negligible. Radiation, the means by 
which this transfer is affected, is a free wave movement of 
some type. It is an oscillatory phenomenon, the space between 
the sun and the receiving body being, so far as is known, en- 
tirely unaffected. The length^ of such oscillations varies from 

^ The approximate wave lengths are as follows: 

Infra-red 000270 to .000075 cm. 

Light waves 000075 to .0000.36 cm. 

Ultra-violet 000036 to .000019 cm. 



226 NATURE AND PROPERTIES OF SOILS 



the short ultra-violet rays, through the so-called light wave 
series to the long infra-red rays, the latter possessing the 
greatest heat possibilities. The insolation of energy received 
at the upper limits of the earth's atmosphere varies with the 
season and with the position chosen.^ 

Due to the gases of the atmosphere and especially to clouds 
and dust, only a small portion of the total insolation actually 



ATMOSPHERE 



/?AD/ANr 
ENEr?GY 

f?£rLECT/0/V 
/?Er/?ACT/ON/ 



SVAPO/?AT/OAr 



nAOlATJ0/\/ 





CONDUCT/ON 
1 



rSEFLECT/ON 



SO/L 




S 1/7? FACE 




CONDUCTION 
COfJVECTlON 
0f?6AhJ!C DECAY 



l-AI350l^PT/ON 
COLO/?, SLOPE 

2-5PECIF/C HEAT 
TEXTUPE 
ST/?UCTUI?E 
MO/STU/?E 

3-MOl/EMENT 

4-LOSS OF HEAT 



(. rise: or 

TEMPERATURE 






Fig. 41. — A diagram showing the heat relations of soil. 

does work either on the land or water surfaces of the earth. 
The atmosphere and its impurities probably deflect on an 
average more than three-fourths of the insolation by absorp- 
tion, reflection, and refraction. Little or none of such energy 
ever reaches the earth itself. Clouds and dust play an im- 
portant role in such interception, affecting to a marked degree 
the energy received at any particular location. Part of the 
original insolation reaching the earth 's surface is immediately 
reflected and is lost as radiant energy, having undergone no 

^ The earth and its atmosphere receives but one two-billionth of the 
sun's energy. CTn such a trifling proportion of the sun's energy depend 
almost all of the earth 's activities. 



SOIL HEAT 227 

transformation and, therefore, having done no work. This 
reflection is much greater on sea than on land and greater 
from snow than from soil surfaces. Reflection is influenced 
to a marked degree by vegetation, stubble, for example, being 
more effective tlian a green field, a forest or even bare soil. 
Possibly one-fifth of the earth's insolation on the average is 
absorbed by the land and water surfaces, being the source of 
the energy which later functions both statically and dynam- 
ically in the soil. 

The statement is often made that warm rain carries con- 
siderable heat into the soil. Such an assertion is not only 
misleading but in most cases entirely incorrect. Precipitation 
in general is usually cooler than the soil in temperate regions, 
especially in the summer. Rain is spoken of as warm, not 
in comparison with soil but with average rain-water tempera- 
ture. Even if rain water should be 10° F. warmer than the 
soil, a very improbable assumption, an average rain would 
raise the temperature of the surface six inches only slightly. 

117. Absorption of insolation. — The energy received 
from the sun functions in a number of ways on reaching the 
land surfaces of the earth. It may accelerate chemical re- 
actions, it may be absorbed by plants, it may induce certain 
changes in form and, lastly, it may be converted into heat. 
It is ip this latter state that insolation energy plays its most 
important part in soil activities, since heat energy may act 
in ways that radiant energy finds impossible. Since heat is 
commonly conceived as the kinetic energy of the molecules 
of a body, it is quite distinct and different from solar radia- 
tion, which must encounter some favorable substance before 
heat is produced. Temperature is the condition of a body 
in respect to its heat energy and is the common mode of ex- 
pressing heat intensity.^ 

* Molecules are in constant motion, colliding with their neighbors, re- 
bounding, and quivering. They possess energj' which is called heat. 
Temperature is determined by the velocity of the molecules and is a 
manifestation of heat. 



228 NATURE AND PROPERTIES OF SOILS 

Certain inherent qualities of the soil as well as its position 
tend to influence its capacity to absorb radiant energy. The 
effect may be measured in the resultant rise in temperature, 
providing all variables are under control. The factors in- 
volved are texture, structure, color, and position. Only the 
last two are of practical importance. 

118. Influence of color on absorption. — It is well known 
that a black surface absorbs more energy than a white 
one under similar conditions and will register a more rapid 
and a higher temperature rise. This is because of a difference 
in reflection, the white surface being more effective in this 
respect. The same principle has been shown by a number 
of investigators to hold with soil.^ The addition of organic 
matter, provided its decomposition has been of the proper 
sort, will, other factors being equal, favor a higher soil tem- 
perature. Wollny- in experimenting with soil covered with 
thin layers of different colored material obtained some inter- 
esting field data. The black soil not only exhibited the high- 
est temperature but also showed the greatest fluctuation. Min- 
imum temperatures were the same regardless of color, while 
temperature differences decreased with depth. The curves 
in Fig. 42 are typical of Wollny's results on clear days. 

Besides the quite obvious effect of color on rate of energy 
absorption, the curves exhibit two other points worthy of 
notice. The first is the tendency of the soil temperature to 
lag behind that of the air and the second is the equal minima 
reached by the two soils. The latter tendency would seem 
to indicate that color has little effect on the radiation of heat 

by soil. 

^Bouyoucos, G. J., An Investigation of Soil Temperature; Mich. Agr. 
Exp. Sta., Tech. Bui. 17, p. 30, 1913. 

Lang, C., tJber Warme-ab sorption und Emission des Boden; Forsch. 
a. d. Gebiete d. Agr.-Physik., Band I, Seite 379-407, 1878. 

^Wollny, E., Untersuchung iiber den Einfluss der Farbe des Bodens 
auf dessen Erwarmuno ; Forsch. a. d. Gebiete d. Agri.-Physik., Band I, 
Seite 43-69, 1878. Also, Untersuohungen iiber den Einfluss der Farbe 
des Bordens auf dessen Erwdrmung ; Forsch. a. a. Gebiete d. Agr.-Phys., 
Band IV, Seite 327-365, 1881. 



SOIL HEAT 



229 



119. The effect of slope on absorption. — The second 
phase to be considered in the rise of temperature of a given 
soil is the angle of incident of the sun's rays. The greater 
the inclination of a soil from a right angle interception, the 
less rapid will be the rise in temperature. As a consequence, 
the total insolation received in the tropics to a unit area is 
greater than that attained by a corresponding area in the 
temperate zone. Moreover, any condition in a temperature 



30 
























?'> 


?i 


















^■"-^c^ 


?0 


5: 

5 








y 




y 




><; 




2Si2^ 


I*) 








/ 




3 


y 






N 


^ 


10 






J 


r 


y^ 


/ 












a 






7^ 


-«£:--' 



























TJ^. 


f£ /N 


HOi/ 


RS 









M 



6 



10 



N 



/O 



Fig. 42. — Curves showing the temperature variations of different colored 
soils at a four inch depth compared with air temperature. Munich, 
June 23, 1876. 

region which tends to bring a unit surface more nearly normal 
to the sun's rays will increase its absorbed energy and raise 
its average seasonal temperature. In the north temperate 
zone this is of course a southerly inclination. The diagram 
(Fig. 43) illustrating conditions on the 42d parallel at noon 
on June 21 makes clear this relationship. 

It is seen that in this case a southerly slope of 20° received 
the greatest amount of heat to a unit area with the level soil 



230 



NATURE AND PROPERTIES OF SOILS 



next and the northerly slope last. The amount of heat for 
a given area is in the order of 106, 100, and 81, respectively. 




Fig. 43. — Diagram showing the distribution of a given amount of radiant 
energy on different slopes on June 21, at the 42nd parallel north. 



These generalizations have been established by the work of 
a number of investigators.^ 

Wollny- found near Munich that the temperature of soutli- 

* King, F. H., Physics of Agriculture, p. 218. Madison, Wis., 1910. 
- Wollny, E., Untersuchungen iiber den Emfluss der Exposition auf die 



SOIL HEAT 231 

ward slopes varied with the time of year. For example, the 
southeasterly inclination was warmest in the early season, the 
southerlj^ slope during mid-season and the southwesterly slope 
in the fall. Such a relationship is of course governed entirely 
by local climatic conditions, especially cloudiness, and might 
not be true of any other place. A southeasterly slope is gen- 
erally preferred by gardeners. Orchardists also pay strict 
attention to the aspect as it is often a factor in sun-scald and 
certain plant diseases. 

120. Rise of temperature and the factors involved. — 
The rise of temperature of a layer of soil following a given 
absorption, depends (1) on the specific heat of the soil, (2) on 
the rate at which the heat moves to other parts of the soil 
mass, and (3) on the losses of heat to the atmosphere. It is 
evident that in a study of the influence of insolation on soil 
temperature, specific heat should receive the first attention. 

121. Specific heat and soil temperature. — The specific 
heat of any material may be defined as its thermal capacity 
compared with that of water. It is expressed as a ratio to the 
quantity of heat required to raise the temperature of a given 
amount of a certain substance 1° C. to the quantity needed 
to change an equal amount of water from 15° to 16° C. 

The specific heat figure for soil generally refers to the heat 
capacity of the dry substance. Under normal conditions, soils 
contain variable amounts of pore spaces and consequently 
have different weights to the cubic foot. A specific heat figure 
based on weight, therefore, does not give a true idea of the 
relative heat capacities of two soils. The expression of spe- 
cific heat by volume seems a more rational basis of compari- 
son.^ The specific heat of the soil is important because of the 
relation it has to the warming up of soil in the spring, the 

Erwdrmung des Bodens; Forsch. a. d. Gebiete d. Agr.-Physik., Band I, 
Seite 263-294, 1878. This publication contains a number of other papers 
on this subject by Wolhiy. 

* Weight specific heat of a substance may be expressed by the number 
of calories required to raise the temperature of one gram, 1° C. Volume 



232 NATURE AND PROPERTIES OF SOILS 

rate of cooling in autumn, drainage influences, and like phe- 
nomena. 

Specific heat data from different investigators do not show 
the agreement that might be expected.^ This is probably due 
(1) to inaccuracies in the naming of the soils used, (2) to 
difference in methods, and (3) to difficulties in technique. 
Everything considered, the following table from Ulrich - dis- 
plays in a suitable way the important specific heat phases: 

Table XLVII 
volume of specific heat of soil 



Soils 



Sand 

Clay.. 

Organic matter. 



Weight 
Volume 



1.52 

1.04 

.37 



Volume 
Specific Heat 



.2901 
.2333 
.1639 



It is evident that specific heat is partially governed by the 

organic matter of the soil and partially by texture and struc- 

specific heat is the number of calories necessary to raise the temperature 
of one cubic centimeter of the substance one degree. In the case of 
soil, weight specific heat may be changed to volume specific heat by 
multiplying it by the volume weight, since volume weight is the weight 
in grams of one cubic centimeter of dry soil. 

^ The following weight specific heats from Lang,* Patten t and Bou- 
youcos t are interesting: 

Lang Patten Bouyoucos 

Coarse sand 198 Sand 185 Sand 193 

Limestone soil. . . .249 Sandy loam .183 Gravel 204 

Organic soil 257 Loam 191 Clay 206 

Garden soil 276 Loam 194 Loam 215 

Peat 477 Clay 210 Peat 252 

* Lang, C, JJher Wiirme Capacitcit der Bodenconstituenten ; Forsch. a. 
d. Gebiete d. Agr.-Phys., Band I, Seite 109-147, 1878. 

t Patten, H. E., Heat Transference in Soils; XJ. S. Dept. Agr., Bur. 
Soils, Bui. 59, p. 34, 1909. 

$ Bouyoucos, G. J., An Investigation of Soil Temperature ; Mich. Agr. 
Exp. Sta., Tech. Bui. 17, p. 12, 1913. 

^Ulrich, R., Untersuchungen iiber WdrmeTcapazitdt der Bodenhonsti- 
tuenten; Forsch. a. d. Gebiete d. Agr.-Phys., Band 17, Seite 1-31, 1894, 



SOIL HEAT 



233 



tnre. Organic matter will lighten and loosen a soil, and lower 
the volume weight. Moreover, its heat capacity is low. The 
effect of such an addition is to lower the specific heat figure. 
It is apparent also that the finer the texture of the soil, the 
lower the specific heat. That is due not to a difference in 
chemical composition but to a lowered volume weight. Any 
practice, therefore, that tends to vary volume weight will in 
a like manner vary specific heat. The farmer may encourage 
the warming of his soil by deep and efficient plowing. By 
increasing its organic content, he may create a tendency in 
the same direction. 

One other factor, more important than those already men- 
tioned, yet remains to be discussed. This is water, so univer- 
sally present in soils and so important in natural soil phe- 
nomena. As the specific heat of water is several times greater 
than that of the soil constituents, any addition of it must raise 
the thermal capacity of the mass. The following data from 
Ulrich^ show that moisture rather than texture and organic 
matter is the controlling factor in normal soil : 



Table XL VIII 

THE EFFECT OF MOISTURE ON VOLUME SPECIFIC HEAT OF SOIL 

(moisture expressed as a percentage of the total water capacity) 





Dry 
Soil 


10%- 
Water 


20% 
Water 


40% 
Water 


60% 
Water 


80% 
Water 


100% 
Water 


Sand 


.291 


.330 
.294 
.242 


.368 
.355 
.320 


.444 

.478 
.476 


.520 
.600 
.632 


.597 
.723 

.788 


.675 


Clay 

Organic matter 


.233 
.164 


.845 
.945 



The overwhelming influence of moisture is at once evident 
from these data. Fine texture, because of its high water 
capacity, usually accentuates the dominance of moisture. 
Organic matter functions in the same way. While an organic 

^ Ulrich, R., Untersuchungen iiher die W drmekapazitat der BodenJconsti- 
tuenten; Forsch. a. d. Gebiete d. Agr.-Phys., Baud 17, Seite 27, 1894. 



234 NATURE AND PROPERTIES OF SOILS 

soil of low volume weight may warm up easily when dry, its 
high water content usually markedly retards its temperature 
change. A muck soil is usually the last to freeze in winter 
and, conversely, the last to thaw in spring. The advantage 
of drainage is evident as a wet soil is of necessity colder in 
the spring than one that is well drained. This at least par- 
tially accounts for the fact that a sandy soil is usually an early 
one and is, therefore, of particular value in trucking. 

122. Heat movements in soil. — While volume weight, or- 
ganic matter, and moisture seem largely to control the degree 
to which a soil will become heated when exposed to insolation, 
it is evident that there must be some mode of energy transfer 
whereby such phenomena may be facilitated. Heat movement 
is necessary in order that the lower layers of the soil may 
become warm enough for proper biological functionings. 
Energy transmission both downward and laterally is abso- 
lutely essential and deserves as much attention as the factors 
influencing insolation absorption. 

Two methods of heat transfer function in a normal soil — 
conduction and convection. These modes of energy move- 
ment are extremely difficult to analyze, due to the impossi- 
bility of controlling one while studying the other. 

123. Conduction of heat in soil. — While radiation has to 
do with the oscillatory transfer of energy conduction relates to 
the molecular transmission of heat through any material. 
When one part of a substance is heated, the movement of its 
molecules is stimulated. These molecules strike their neighbors 
with increased force, thus quickening their motion. These in 
turn accelerate others until the energy applied at one point 
becomes apparent at another. Solids as a class are better con- 
ductors than liquids, while liquids in general are superior to 
gases in this respect. It must be remembered in studying the 
conductivity of heat through soil, that we are dealing with 
a heterogeneous mixtvire of mineral and organic matter con- 
taining varying amounts of air and water. The movement 



SOIL HEAT 235 

of soil heat involves not only the question of conduction 
througli solids but through liquids and gases as well. More- 
over, transfer resistance, which occurs at the boundary of two 
substances in contact, has much to do with the rate of trans- 
mission. In addition, the air and water of the soil are capable 
of considerable movement which makes conductivity studies 
extremely difficult due to convection currents. 

The heat conductivity of soil is aifected by a number of 
factors which may or may not lend themselves to field con- 
trol. Important among these are texture, structure, organic 
matter, and moisture. The influence of the first is clearly 
shown by the following comparative data obtained by Bou- 
youcos,^ with field soils: 

Table XLIX 

relative conductivity as measured by the time required 

for a thermometer 7 inches from the source of heat 

to indicate a rise in temperature 



Soil 



Relative Rate 
OF Conductivity 



Sand. 
Loam , 
Clay. 
Peat. 



100 
150 
143 
362 



These results are comparative only in a qualitative way. 
Quantitative determinations are so beset by error that only 
few investigators have made any consistent attempt along this 
line. Patten's results^ expressed as metric K ^ (the heat con- 

* Bouyoucos, G. .T., An Investiqation of Soil Temperature; Mich. Agr. 
Exp. Sta., Tech. Bui. 17, p. 20, 1913. 

=" Patten, H. E., Heat Transfer in Soils; U. S, Dept. Agr., Bur. Soils, 
Bui. 59, p. 26-28, 1909. 

^ The conductivity of a substance is measured by the number of gram- 
calories of heat transmitted in 1 second through a cube with 1 centi- 
meter edges, when the opposite faces differ in temperature by 1°C. The 
calories of heat transmitted (H) will be proportional to the area of the 



236 NATURE AND PROPERTIES OF SOILS 

ductivity coefficient in C.G.S. units) shows the same general 
comparisons as already presented: 

Table L 
conductivity coefficients of different dry soils 



Soils 



Coarse quartz 

Leonardtown loam 

Podunk fine sandy loam. 

Hagerstown loam 

Galveston clay 

Muck 



K 



.000917 

.000882 
.000792 
.000699 
.000577 
.000349 



It is evident, in general, that the finer the texture of the 
soil, the lower is the conductivity. This cannot be construed 
as indicating that the conductivity coefficients of sand and 
clay particles are particularly different. The variance ob- 
served is adequately explained by the great number of trans- 
fers necessary in a fine-textured soil. It is also evident that 
the addition of organic matter will lower conductivity. 
Humus itself has a low conductivity coefficient and would 
markedly affect the transfer resistance by changing the struc- 
ture of the soil. Compacting a soil should accelerate heat 
transfer due to a more intimate contact of the soil grains and 
a consequent diminution of transfer interference. Tillage, 
on the contrary, must impede not only the movement of heat 
downward in the soil but from the subsoil into the furrow 
slice. 

The greatest single factor to be considered in heat conduc- 
tivity is the moisture content of the soil. The curve (Fig. 44) 

faces (A) and to the differences in temperature of the faces (f — t"), 
while it will be inversely proportional to the thickness (d) of the cube. 
K is a constant, depending on the material studied. 



SOIL HEAT 



237 



for fine sandy loam, constructed from Patten's data/ illus- 
trates its effect and indicates how heavily it must override the 
factors already mentioned: 



, 00$00 














C 


X 









-/- 




I 








/ 




>. 








/ 




bw 








/ 




i^ 








/ 




k> 






J 






^ 






^^ 






o 






^^^ 






^ 




^^ 


^^''^ 






s> 














^ 


^ 








y 


PERCEJ\/'j 


'" OF MC 


iJSTUJRE 


IN 30/L 





,00400 



.00300 



.00200 



.00100 



^ /O I^ 20 25 

Fig. 44. — Conductivity curve for Podunk fine sandy loam, showing the 
influence of moisture content upon the rate of heat transfer. The 
curve apparently flattens out at a high moisture content indicating 
that good conductivity may be obtained at optimum moisture. 

At first glance it appears peculiar that the heat movement 
through a soil, the mineral constituents of which possess a 
conductivity coefficient of about .01066, should be accelerated 
by the addition of a liquid possessing a value for K of about 
.00149. The explanation lies in the lowering of the transfer 

^ Patten. H. E., Heat Transfer in Soils; U. S. Dept. Agr., Bur. Soils, 
Bull. 59, p. 27, 1909. 



238 NATURE AND PROPERTIES OF SOILS 

resistance. Heat passes from soil to water about 150 times 
easier than from soil to air. As the water increases, the air 
decreases and the rate of conductivity is raised. When suf- 
ficient water is present to join all of the soil particles, further 
additions will have little effect on character of heat movement. 
Moisture, optimum for crop growth, amply provides for heat 
transfer. The slow warming up of the lower subsoil must not 
be taken as an indication of lower conductivity. It is due 
rather to a lessened heat supply. As a matter of fact, the 
rate of heat transmission has been shown to be more rapid in 
the subsoil, due to a greater compaction and to the presence 
of more water. 

This brief discussion of conductivity shows the vital im- 
portance of such a phenomenon to plants in that the necessary 
heat is carried broadcast through the soil. While conduc- 
tivity is affected to a certain extent by texture, structure, and 
organic matter, moisture is the dominant factor. Under nat- 
ural conditions, it is necessary to maintain a medium amount 
of water in the soil. This moisture condition, fortunately, 
supports almost maximum heat conduction. Good tilth and 
increased organic matter probably exert their greatest in- 
fluence on this type of heat transfer by their influence on soil 
moisture. 

124. Convection transfer of heat. — Convection, the third 
manner by which energy may be conveyed, is a heat transfer 
by means of currents in liquids or gases. It functions by an 
actual and obvious movement of matter. In the soil absorp- 
tion tends to heat the air as well as the solid substance. This 
produces currents due to the expansion and rise of the warmed 
gases. It is obvious that such heat movement must always be 
lateral or upward, never downward. Such convection exerts 
its greatest influence in equalizing the temperature of the soil, 
overcoming the effects of unequal conduction and uneven ab- 
sorption due to vegetation or stone. Air currents as they 
escape into the upper air carry considerable heat away from 



SOIL HEAT 239 

the soil. Such a loss is of little moment, however, compared to 
that continually occurring through conduction and radiation. 

Some heat is carried downward into the soil by percolat- 
ing water. This is a true convection activity. The impor- 
tance of such a heat transfer is only conjectural. As percola- 
tion is generally intermittent in a soil, it is probable that it 
does not modify to any extent the influence exerted by con- 
duction. 

125. Effect of organic matter on soil temperature. — 
Plants entrap a considerable amount of radiant energy from 
the sun, part of which is utilized during the growth period. 
The remainder exists as latent energy in the tissue. If any 
amount of plant remains are incorporated in the soil and de- 
cay proceeds, this heat is liberated. Thus a heat transfer is 
similar in a way to convection, except that, in this case, the 
transfer is by the movement of a solid and the energy is 
latent. 

To what extent the decay of organic matter is effective in 
bringing about any important modification of field soil, it is 
difficult to say. In greenhouses and hotbeds perceptible in- 
creases are obtained by the use of fresh manure. In the field, 
however, where the absorption and loss of heat are very large 
and where the organic matter makes up but a small portion 
of the soil mass, it is doubtful whether any important heat 
increase occurs. Georgeson,^ in Japan during the first twenty 
days after an application of eighty tons of manure to the 
acre, obtained an increase of only 3.4° F. over a soil un- 
treated. Wagner ^ found an average increase of 1° F. from 
the use of twenty tons of barnyard manure to the acre. Bou- 
youcos ^ has obtained the latest data on the subject. Under 

' Georgeson, C. C, Influence of Manure on Soil Temperature; Agri. 
Sci., Vol. 1, pp. 2.5-.52, 1887. 

' Wagner, F., Pher den Einfluss der Bungung mit Organischen Sub- 
stance auf die Bodentemperatur ; Forsch. a. d. Gebiete d. Agr.-Phys., 
Band V, Seite 373-405, 1882. 

* Bouyoucos, G. J., An Investigation of Soil Temperature ; Mich. Agr. 
Exp. Sta., Tech. Bui. 17, pp. 180-190, 1913. 



240 NATURE AND PROPERTIES OF SOILS 

carefully controlled conditions, he found that unless excessive 
amounts of manure were added no appreciable effects were 
observed. Such results indicate that the heat of decay and 
fermentation has little practical effect in modifying the tem- 
perature of field soils. AVithout doubt there are certain local- 
ized influences, but how important they may be is beyond 
our present knowledge. As far as heat relations are con- 
cerned, it seems that organic matter exerts its greatest effects 
through a darkening of the color and an increase in the mois- 
ture capacity of the soil, 

126. Loss of heat — conduction, radiation, and evapora- 
tion. — Although small amounts of heat may be carried from 
the soil by percolating water, the only important loss is into 
the atmosphere above. This loss occurs in three ways, con- 
duction, radiation, and evaporation. The loss due to evapora- 
tion is easily the least important of the three. Conduction 
and radiation have much to do with climatic control, since 
the atmosphere receives its energy in large degree from the 
earth rather than directly ■ from the sun. Conduction from 
soil to air and vice versa can be modified but to a slight extent 
by man, a fortunate provision of nature. 

Terrestrial bodies are continually radiating energy waves 
into the atmosphere, the change of temperature depending on 
whether the receipt of such oscillations exceeds or falls short 
of the loss. In the case of the soil, there is a very great dis- 
sipation of energy in this way, radiation with conduction 
being important climatic controls. The rapid changes in air 
temperature are often directly due to these phenomena. 

These energy waves of terrestrial origin are very long,^ 

being within the infra-red group and consequently make 

no impression on the eye. They are often spoken of as the 

dark rays. Their energy capacity is higher than that of 

shorter oscillations. The trapping of heat in a greenhouse 

* Terrestrial bodies at ordinary temperatures give out waves varying 
in length from .000270 to .001500 cm. The warmer the body, the shorter 
the wave length. 



SOIL HEAT 241 

is partially due to the tendency of the objects within the house 
to give off these long rays, which do not pass through the 
glass with the facility possessed by the shorter vibrations by 
means of which a large proportion of the energy was intro- 
duced. 

The texture, structure, and color of the soil have little in- 
fluence on radiation. Moisture tends to hasten it a trifle, 
since water is a better radiator than soil. Mulches, as they 
are loose and dry, may check radiation slightly. Artificial 
coverings, shelters, and clouds seem to exert the greatest effect. 
It is often feasible to protect plants from frost by interfering 
with radiation and conduction. Clouds by shutting in heat, 
may in some cases prevent a frost that would otherwise occur, 
due to the rapid cooling. Snow likewise has a protecting 
effect and may often prevent the soil underneath from freez- 
ing. While man may influence radiation locally, it is evident 
that the total energy loss can be checked but little. 

The effect of evaporation on the temperature of the soil is 
especially noticeable because of its rapid action. This vapor- 
ization of water is caused by an increased molecular activity 
and requires the expenditure of a certain amount of heat,^ 
which results in a cooling effect on the water remaining and 
consequently on the soil and air with which it is in contact. 
It requires 267.9 kilogram calories to evaporate one pound 
of water at 50° F. This is sufficient to lower the temperature 
of a cubic foot of saturated clay about 20° F., providing that 
all of the energy of evaporation comes from the soil and its 
water. 

The low temperature of a wet soil is due partially to evapo- 
ration and partially to high specific heat. King ^ found during 

* It requires 536.6 gram-ealories to evaporate one gram of water at 
100°C., while 596.7 calories are necessary if evaporation takes place at 
0°C. The calories (C) required to vaporize one gram of water at any 
temperature (t) may be calculated by the formula: 
C = 596.73 — .601 t 

*King, F. H., Physics of Agriculture, p. 20; Madison, Wia., 1910. 



242 NATURE AND PROPERTIES OF SOILS 

April that an undrained soil in Wisconsin ranged from 2.5°F. 
to 12.5° F, lower than one of the same type well drained. 
Parks ^ reports data of the same order from England. Drained 
and undrained soil held in trays at Urbana, Illinois,- showed 
maximum differences of 13.7° F., 9.0° F., and 6.2° F. at 
depths of 1, 2, and 4 inches, respectively. The differences 
were greatest in the day. Wollny considers that the depres- 
sion of temperature due to evaporation is roughly propor- 
tioned to the moisture present. Texture, structure, and or- 
ganic matter influence the cooling action of evaporation, since 
they exert such a marked effect on water capacity and capil- 
lary movement. The practical importance of evaporation 
study lies in the fact that it can be controlled to such a 
marked extent in the field. Such is not true of radiation and 
conduction. Windbreaks and shelters have been shown by 
King ^ to reduce evaporation over short distances as much as 
25 per cent. This means a conservation of soil energy for 
the time being. Thorough under-drainage not only checks 
evaporation losses but lowers the specific heat of the soil, 
retards its radiation and facilitates convection. This means 
a faster warming up, especially of the root zone. Optimum 
moisture encourages optimum heat conditions as well as other 
favorable phenomena. Drainage, tillage, and organic matter 
are the dominant factors in this moisture control. 

127. Soil temperature and its variations. — The tempera- 
ture of the soil at any time depends on the ratio of the energy 
absorbed and the heat being lost. The constant change in 
this coordination is reflected in the seasonal, monthly, and 
daily soil temperatures. The following data * are representa- 

* Parks, J., On the Influence of Water on the Temperature of Soils; 
Jour. Roy. Agr. Soc. Eng., Vol. 5, pp. 119-146, 1845. 

^Hosier, J. G., and Gustafson, A. F., Soil Physics and Management; 
p. 302; Philadelphia, 1917. 

'King, F. H., The Soil, p. 189; New York, 1906. 

*Swezey, G. D., Soil Temperatures of Lincoln, NebrasTca; Nebr. Agr. 
Exp. Sta., 16th Ann. Rep., pp. 95-102, 1903. 



SOIL HEAT 



243 



tive of soil temperatures in temperate climates with moderate 
rainfall : 

Table LI 

AVERAGE TEMPERATURE READINGS TAKEN AT LINCOLN, 
NEBRASKA, 1890-1902. DEGREES FAHRENHEIT 







1 


3 


6 


12 


24 


36 


Season 


Air 


Inch 


Inches 


Inches 


Inches 


Inches 


Inches 






Deep 


Deep 


Deep 


Deep 


Deep 


Deep 


Summer. . . 


25.9 


28.8 


28.8 


29.5 


32.2 


36.3 


39.1 


Autumn . . . 


49.9 


54.8 


53.6 


51.6 


48.5 


45.7 


44.3 


Spring. . . . 


73.8 


83.0 


80.9 


79.1 


73.8 


69.0 


66.2 


Winter. . . . 


53.9 


56.4 


57.6 


57.1 


57.5 


59.3 


60.3 



It is apparent that the seasonal variations of temperature 
are considerable even at the lower depths. The surface layers 
vary more or less in accord with the air temperature and, 
therefore, exhibit a greater fluctuation than the subsoil. In 
general, the surface soil is warmer in spring and summer than 
the lower layers but cooler in fall and winter. The soil, on 
the average, is warmer than the air in winter. This occurs 
because the air responds more quickly to a change in solar 
insolation than the soil. 

The curves showing the monthly march of soil temperature 
at Lincoln, Nebraska (Fig. 45), reveal the lag of the tempera- 
ture change in the subsoil due to slow heat penetration. It is 
also noticeable that the monthly range in temperature change 
in the surface soil is higher than that of the air. The abso- 
lute range is, of course, greater for the air. It must be kept 
in mind that changes in soil temperature are gradual, while 
the air may vary many degrees in an hour. 

The daily and hourly temperature of the air and soil in 
the temperate zone may show considerable agreement or 
marked divergence according to whether the weather control 
is cyclonic or solar. With solar control and a clear sky the 
air temperature rises from morning to a maximum at about 



244 NATURE AND PROPERTIES OF SOILS 

two o'clock. It then falls rapidly. The soil, however, does 
not reach its maximum temperature until later in the after- 
noon, due to the usual soil lag. This retardation is greater 
and the temperature change less as the depth increases.^ The 
substratum of a soil shows little daily, or even monthly, varia- 
tion and is affected, if at all, by seasonal changes only. The 




JAN. FE8R. MAR. APR. MAV JUNE JULY AUG. SEPT. OCT, NOV^ DEC. 



Fig, 45. — Curves showing the average monthly temperature readings at 
various soil depths. Average of twelve years, Lincohi, Nebraska. 

curves in Fig. 46, comparing soil and air temperatures at 
Munich^ on a bright day in May, substantiates some of the 
statements above : 

128. Control of soil temperature. — The most important 
factor in the control of soil heat is obviously moisture. Good 

^ The following lavrs hold in a general way : 

1. The lag of the temperature wave is proportional to the depth. 

2. The diurnal amplitude of the temperature oscillation decreases in 
geometric progression as the depth increases in arithmetic progression. 
If the temperature variation at the surface was 24°F and at 6 inches 
deep 12°F, according to this law the diurnal variation at 12 inches 
would be 6°F and at 18 inches 3°F. 

^Wollny, E., Untersuchungen iiber den Einfluss der PflanzendecTce und 
der BescliatUinq auf die Physilalischen Eigenschaften des Bodcn; 
Forsch. a. d. Gebiete d. Agr.-Physik., Band VI, Seite 197-256, 1885. 



SOIL HEAT 



245 



drainage, and a proper structural development, sufficient or- 
ganic matter and deep and careful plowing, favor optimum 
moisture conditions. Such moisture regulation means a low- 
ered specific heat, rapid conductivity, and good convection. 
The increase of soil organic matter may act directly in heat 
control by darkening the color and thus increasing absorp- 



S5 
60 

75 
70 
65 
60 



55 



50 

































/ 


^ 






\ 






IW 








A 








\ 


V 


^ 








/ 




'h 








\ 


N 


}? 

s 






/ 




/ 










\ 


^^ 




/ 






/ 










\ 






/ 


-^ 
















"^ 




/ 




T/M£ 


IN MR 


s. 











Af 



S 



JO 



/V 



Fig. 46. — Curves showing the hourly temperature of a bare soil at a 
depth of four inches and of the air just above the soil in Ger- 
many, May 26. (Data from Wolhiy.) 



tion. A soil-mulch, being dry, not only may check evapora- 
tion but at the same time may lower radiation. 

Any method of handling the land which tends to benefit its 
physical condition, better its tilth and control its moisture, 
tends at the same time towards a proper heat control. The 
whole question may be summarized by saying that, if a farmer 
adopts a proper system of moisture control and at the same 
time employs methods that continually encourage a better 



246 NATURE AND PROPERTIES OF SOILS 

physical condition of the soil, the problem of the control of 
soil heat will be solved automatically. The farmer will then 
have brought about the best conditions for heat absorption 
and will have facilitated conduction and convection, retarding 
at the same time losses by evaporation and radiation. 



CHAPTER XII 
SOIL AIR 

The soil is a porous mass of material of which only about 
one-half is solid matter. The pore space that results is occu- 
pied by water and by air in a constantly varying proportion. 
When a soil is in good condition for crop growth, the air 
space rarely makes up more than from 20 to 25 per cent, of 
its volume. The texture of the soil and the amount of mois- 
ture are obviously the main controls. The individual air 
spaces of the soil are more or less continuous and seem to 
maintain a fairly complete communication between the vari- 
ous horizons. The better the granulation of the soil and 
the greater the number of cracks and burrows, the easier and 
quicker is this communication. The air of the soil is either 
directly in contact with the roots and the soil bacteria or 
separated from them by only a thin layer of moisture or col- 
loidal material. 

The air of the soil is not merely a continuation of the atmo- 
spheric air into the interstitial spaces. As it is enclosed by the 
soil complexes and by the soil-moisture movement does not 
take place readily. Hence it is greatly influenced by its local 
surroundings. This leads to important differences between 
the atmospheric air and the soil air, the character of the latter 
depending on a variety of conditions in which the physical, 
chemical and biological properties of the soil play a large 
part. 

129. Composition of soil air. — The air of the soil differs 
from that of the outside atmosphere in that it contains more" 
water-vapor, a much larger proportion of carbon dioxide, a 

247 



248 



NATURE AND PROPERTIES OF SOILS 



correspondingly smaller amount of oxygen, and slightly larger 
quantities of other gases, including ammonia, methane, hydro- 
gen sulfide, and the like, formed by the decomposition of 
organic matter. The percentage of nitrogen is practically the 
same in all cases. The following average data quoted from 
three different sources show the comparative compositions 
as far as the carbon dioxide, oxygen, and nitrogen are con- 
cerned. All other gases are included with the nitrogen fig- 



ures. 



Table LIT 



AVERAGE COMPOSITION OF SOIL AIR AND ATMOSPHERIC AIR 





Percentage by Volume 




CO, • 


0. 


N. 


Soil Air 

Germany ^ 

Iowa ^ 


.20 
.20 
.25 

.03 


20.60 
20.40 
20.65 

20.97 


79.20 
79.40 


England * 

Atmospheric Air 
England * 


79.20 
79.0 



Russell and Appleyard,^ in their study of the soil atmo- 
sphere, found that there are really two types of soil air. The 
first one occupies the portion of the pore space not taken 

* Atmosphere air carries about .93 per eent. of argon, with very small 
amounts of other inert gases such as krypton, xenon, helium and neon. 
These gases are of course present in the soil. 

"Lau, E., Beitrdge zur Kenntnis der Zusammensetsung der im Acker- 
hoden bepidlichen Luft; Inaug. Diss., Eostock, 1906. 

^Jodidi, S. L., and Wells, A. A., Influence of Various Factors on 
Decomposition of Soil Organic Matter; la. Agr. Exp. Sta., Res. Bui. 
No. 3, Oct. 1911. 

* Russell, E. J., and Appleyard, A., The Atmosphere of the Soil: Its 
Composition and the Causes of Variation; .Tour. Agr. Sci., Vol. VII, 
Part 1, pp. 1-48, 1915. 

= Russell, E. J., and Appleyard, A., The Atmosphere of the Soil: Its 
Composition and the Causes of Variation; Jour. Agr. Sci., Vol VII, 
Part 1, pp. 1-48, 1915. 



SOIL AIR 249 

up by water, is free to move from place to place and is satu- 
rated or nearly saturated with water-vapor. It is the soil 
atmosphere most commonly referred to and its composition 
is set forth in the above tabulation. After this air was drawn 
off Russell and Appleyard found that still more air could 
be removed by applying suction. This air at first carried 
considerable oxygen but by continuing the suction almost pure 
carbon dioxide was obtained. The amount of gas removed 
by lowering the pressure varied directly with the moisture 
content of the soil and consequently it may be considered as 
air largely absorbed by the moisture of the soil complexes. 

Two types of atmosphere, therefore, exist in the soil. One, 
the ordinary soil air, is comparatively rich in oxygen. The 
other, absorbed by the soil moisture, is very low in oxygen 
but very high in carbon dioxide. Obviously they insensibly 
merge. The biological significance of these atmospheric types 
is very important. Their simultaneous presence admits of 
both aerobic and anaerobic biological activity. For example, 
rapid nitrate formation might be progressing but no accumu- 
lation would be evident, due to just as rapid a synthetic activ- 
ity of the anaerobic forms.^ 

It must not be assumed from the data above quoted that 
the composition of the soil air is at all constant or that it is 
approximately the same in every soil. The soil is dynamic 
in nearly every phase and is nowhere more changeable than 
in its atmospheric composition. This variability will of course 
be more marked and more important in the air which occupies 
the interstitial spaces, although the absorbed air will show 
some fluctuation. The compositions of the air of several soils, 
as determined by Boussingault and Lewy^ are quoted in the 
following table : 

* Gainey, P. L., Beal and Apparent Nitrifying Power of Soils; Science, 
N. S., Vol. 39, pp. 35-37, 1914. 

Doryland, C. .T. T., Influence of Energy Material upon the Relation of 
Soil Microorganisms to Soluble Plant Food; N. Dak. Agr. Exp. Sta., 
Bui. 116, pp. 818-399, 1916. 

* Johnson, S. W., How Crops Feed, p. 219; New York, 1891. 



250 NATURE AND PROPERTIES OF SOILS 



Table LIII 






Character of Soil 


Percentage by Volume 




COa 


0, 


N, 


Sandy subsoil of forest 

Loamy subsoil of forest 

Surface soil of forest 

Clay soil 


.24 
.79 
.87 
.66 
.74 
1.54 
3.64 


19.66 
19.61 
19.99 
19.02 
18.80 
16.45 


79.55 
79.52 
79.35 


Soil one year after manuring 

Soil freshly manured 

Vegetable mold compost 


80.24 
79.66 
79.91 



The differences in the composition of the atmosphere of 
different soils and the variability noticeable within the same 
soil are due primarily to two factors: (1) the production of 
carbon dioxide, and (2) oxidation. These will be discussed 
in the above mentioned order. 

130. The carbon dioxide of the soil air. — The presence 
of carbon dioxide in soils may be due in small part to in- 
filtration from the atmospheric air, there being a tendency 
for the carbon dioxide, which is heavier than nitrogen and 
oxygen, to settle out. It may also have a purely chemical 
origin. The latter source is much more probable. The ab- 
sorption of the bases of carbonates or bicarbonates would 
obviously release carbon dioxide. This probably does not take 
place, however, to any great extent in a natural soil. When 
ground limestone is added, such a reaction does occur.^ Car- 
bon dioxide in appreciable amounts might for a short time 
thus be liberated through chemical reaction. The addition 



^Maclntire, W. H., The Carbonation of Burnt Lime in Soils; Soil 
Sci., Vol. VII, No. 5, pp. 325-446, 1919. See also. The Non-existence 
of Magnesium Carbonate in Humid Soils; Tenn. Agr. Exp. Sta., Bui. 
107, 1914. 



SOIL AIR 



251 



of lime has been shown by several investigators to increase 
the carbon dioxide production/ 

There is now no doubt tbat biological activities are largely 



4.5 


1 ; 

' ■ — " 


N ! 


4.0 


1 i/ 






> 


^.5 




^ 


N^ 


/ 






1 \ 


K 


^0 


]/ 




\ 


r 






y 


\! 


\ 


^ 


?F) 




r 1 


A 


\ 


s. 


1 


/ 




<r 


K 


. 


\ 


g?.n 


/&' 


^[^ 


/^ 




\ 


/^ 












\\ 


o 




V 1 




















V 


I.fi 






















\ 


^ 


.^ 


(-^ 
























































JUNE 



JULY 



AUGUST 



SEPT. 



Fig. 47. — Diagram showing the amount of carbon dioxide in air from 
Volusia silt loam limed and unlimed and cropped to oats. 



responsible for the occurrence of the large quantity of carbon 
dioxide in the soil air. There are two distinct processes in- 

^Bizzell, J. A., and Lyon, T. L., The Effect of Certain Factors on 
the Carbon Dioxide Content of Soil Air; Amer. Soc. Agron., Vol. 10, 
No. 3, pp. 97-112; Mar. 1918. 

Potter, E. S., and Snyder, E. S.^ Carbon Dioxide Production in Soils 
and Carbon and Nitrogen Changes in Soils Variously Treated; la. Agr. 
Exp. Sta., Ees. Bui. 39; Feb. 1916. 

Plummer, J. K., Some Effects of Oxygen and Carbon Dioxide on Nitri- 
fication and Ammonification in Soils; Cornell Agr. Exp. Sta., Bui. 384; 
Dec. 1916. s f , 



252 NATURE AND PROPERTIES OF SOILS 

volved: (1) the physiological action of bacteria by which 
they absorb oxygen and give off carbon dioxide, and (2) the 
excretion of carbon dioxide by roots. (See Fig. 47.) 

Recent work^ has clearly shown that higher plants, espe- 
cially during their most rapid growth, markedly increase the 
amount of carbon dioxide gas in the soil. Stoklasa^ concluded 
that the microorganisms in an acre of soil to a depth of four 
feet may produce between sixty-five and seventy pounds of 
carbon dioxide a day for two hundred days in the year, and 
that during the growing period the roots of oats or wheat 
would give off nearly as much more. Turpin^ finds that the 
crop often produces, during its period of active growth, many 
times as much carbon dioxide as is produced by soil organ- 
isms. He minimizes the influence of the decaying root par- 
ticles of the crop occupying the soil on the carbon dioxide 
content of the soil air. 

In any particular soil, the two major controls of carbon 
dioxide production seem to be temperature and rainfall.* The 
former apparently is dominant in a temperate humid region 
from November to May. During the remainder of the year, 
the moisture content of the soil and the amount of rainfall 
are the direct controls. Bacterial numbers and nitrate ac- 

^ Stoklasa, J., and Ernestj A., Beitrage zur Losung der Frage der 
CJiemischen Natur des JVurzelsekretes ; Jahr. Wiss. Bot., Bd. 46j Seite 
55-102, 1909. 

Aberson, J. H., Ein Beitrag sur Kenntnis der Natur der Wurselaiis- 
scheidunger ; Jahr. Wiss. Bot., Bd. 47, Seite 41-56, 1910. 

Russell, E. J., and Appleyard, A., The Influence of Soil Conditions 
on the Becomfosition of Organic Matter in the Soil; Jour. Agr. Sci., 
Vol. VII, Part 3, pp. 385-417, 1917. 

Bizzell, J. A., and Lyon, T. L., The Effect of Certain Factors on 
the Carbon Bioxide Content of Soil Air; Amer. Soe. Agron., Vol. 10, 
No. 3, pp. 97-112, Mar. 1918. 

^ Stoklasa, J., Methoden sur Bestimmung der Atmungsintensitdt der 
Balcterien im Boden. Zeit, f. d. Landw. Versuchswesen in Oesterreich, 
Band 14, Seite 1243-79, 1911. 

^ Turpin, H. W., The Carhon Bioxide of the Soil Air; Cornell Agr. 
Exp. Sta., Memoir 32, April 1920. 

^ Eussell, E. J., and Appleyard, A., The Atmosphere of the Soil: Its 
Composition and the Causes of Variation; Jour. Agr. Sci., Vol. VII, 
Part 1, pp. 1-48, 1915. 



SOIL AIR 



253 



cumulation seem to fluctuate with the carbon dioxide, while 
the oxygen curve is almost the exact reciprocal. Other in- 
fluences of a minor nature enter in, such as the character of 
the crop growing on the soil, hea\y rainfall, oxygen dissolved 
in the rain, and rapid changes of temperature. (See Fig. 
48.) 

While plowing, application of lime, drainage, and other 
practices have a great influence on the proportion of oxygen 




FEBR. MARCH APRIL. 



MAY 



JUNE JULY 



AUG, 



Fig. 48. — Carbon dioxide in air from Dunkirk clay loam bare and from 
the same soil cropped to oats, 1918. (After Turpin.) 



and carbon dioxide in the soil air, the addition of organic 
matter seems to have the most profound effect. At the 
Rothamsted Experiment Station,^ the carbon dioxide content 
of the air from two soils was studied. One soil (Broadbalk 
field) had been manured for a number of years while the other 
(Hoos) had not received such a treatment: 

^Russell, E. J., and Appleyard, A., The Atmosphere of the Soil: Its 
Composition and the Causes of Variation; Jour. Agr. Sci., Vol. VII, 
Part 1, p. 25, 1P15. 



254 NATURE AND PROPERTIES OF SOILS 

Table LIV 

effect of farm manure on the carbon dioxide content of 
soil air. rothamsted, england 



Treatment 


Percentage of CO2 by Volume 




May 15 


May 25 


June 10 


June 12 


July 7 


July 27 


Manured soil 

Unmanured soil. . . 


.22 
.10 


.32 

.07 


.17 

.08 


.36 
.07 


.36 
.08 


.35 
.09 



Although the formation of carbon dioxide in the soil is in- 
fluenced to a marked degree by the decomposition of organic 
matter, the effect is by nO means proportional to the quantity 
of organic matter present. The rate of decomposition varies 
greatly, and where this is depressed, as sometimes occurs in 
muck or forest soils, the content of carbon dioxide is relatively 
low. A high percentage of organic matter is in itself likely 
to prevent a proportional formation of carbon dioxide, since 
the accumulation of the gas may inhibit further activity of 
the decomposing organisms. 

131. Oxidation and its effect on the composition of the 
soil air. — Oxidative processes in the soil are of two general 
types, those due to chemical reactions alone and those due 
to biochemical transformations. The purely chemical oxida- 
tion may be illustrated best by recalling the processes of soil 
formation.^ Here it was noted that certain minerals, espe- 
cially those carrying iron, were susceptible to the influence of 
oxygen. The following reactions show how olivine may as- 
sume water and then produce ferric oxide through oxidation : 
3MgFeSi04 + 2H,0 = H.MggSi^Og + SiO^ + 3FeO 
4F"eO + 0, = 2Fe203 

This is illustrative of the complex reactions which are con- 
tinually taking place and which tend materially to decrease 
the oxygen of the soil air. 

^ See Chapter II, par. 16, of this text. 



SOIL AIR 255 

Biochemical oxidation, however, is usually rapid and is a 
much more important factor in the oxygen control of the air. 
Not only do all bacteria require oxygen for their growth, ])ut 
they are continually producing compounds that require oxy- 
gen in their molecules. Carbon dioxide is an oxidation 
product. Its formation reduces the oxygen of the air and its 
presence causes a dilution. Sulfofication and nitrification are 
well known examples. The reactions for the process of nitri- 
fication illustrate in addition the production of carbon dioxide 
by chemical means: 

2NH3 -f 30, = 2HNO2 + 2H,0 

2HNO2 + CaCOg = Ca(N0o)2 + H^O + CO2 

Ca(N02)o + Oo = Ca(N03)2 

132. Function of the carbon dioxide of the soil. — The 

solvent action of carbon dioxide is probably one of its most 
important functions in the soil. Constant biological activities, 
combined with the seasonal cropping influences, maintain this 
solvent and keep it continually in contact with the solution 
surfaces of the soil. Althougli a very weak acid when dis- 
solved in water, its rapid formation and continuous action is 
productive of marked effects. 

The availability of almost all of the plant nutrients is due 
either directly or indirectly to the action of carbon dioxide. 
Its influence on the potash of orthoclase, the phosphoric acid 
of tri-calcium phosphate and the calcium of calcium carbonate 
are well known examples: 

2KAlSi308 + 2H.0 + CO^ = H^ALSioO^ + 4Si02 + K0CO3 

CagCPOJ^ + 2H,0 + 2CO2 = CaH,(P0Jo + 2CaCb3 

CaC03 + H2O + CO2 = CaH^ (063)2 

Stocklasa^ has correlated the carbon dioxide production 

*Stoklasa, J,, Metlioden zur Bestimmung der Atmungsintensitdt der 
Bakterien im Boden; Zeit. f. d. Landw, Versuchswesen in Oesterreich, 
Band 14, Seite 1243-79, 1911. 



256 



NATURE AND PROPERTIES OF SOILS 



with the quantity of phosphates found in the drainage water 
from certain soils. Some of his results are given in Table LV : 

Table LV 



Eelative Produc- 
tion OF CO2 
(milligrams to a 
pound of soil in 24 

HOURS) 




Loam 
Clay 

Lime soil 
Organic soil 



11 

7 
16 
25 



Stoklasa considers that the production of carbon dioxide 
is a measure of the intensity of bacterial action in the soil, 
and that in consequence of this activity the phosphorus is 
rendered soluble. 

As far as biological activity is concerned, carbon dioxide 
seems to be a factor only insofar as it dilutes the oxygen.^ 
This seems to be especially true of those bacterial processes 
involved in the formation of nitrates. When it exists to the 
exclusion of the oxygen, it produces anaerobic conditions but 
in this respect it functions in exactly the same way as does 
nitrogen or any other inert gas. Physiologically it seems to 
have no detrimental effects. Carbon dioxide increases so 
markedly with an increase in nitrate production that its 
presence can not be depressing.- 

133. Importance of oxygen in the soil air. — Oxygen is 
the all-important gas of the soil air. Without it no weather- 

^ Plummer, J. K., Some Effects of Oxygen and Carbon Dioxide on 
Nitrification and Ammonification in Soils; Cornell Agr. Exp. Sta., Bui. 
384, Dec. 1916. 

Also, Owen, W. L., Effect of Carbonates upon Nitrification; Ga. Agr. 
Exp. Sta., Bui. 81, 1908. 

^ Neller, J. E., Studies in the Correlation Between the Froduction 
of Carbon Dioxide and the Accumulation of Ammonia by Soil Organ- 
isms; Soil Sci., Vol. V, pp. 225-241, 1918. 

Stoklasa, Julius, Methodcn sur biochemischen TJntersuchung des 
Bodens; Handb. Biochem. Arbeitsmeth., Bd. 5, S. 843-910, 1912. 



SOIL AIR 257 

ing would occur, no minerals would break down, and no solu- 
tion would be possible. Oxidation must go on rapidly and 
continuously in the normal soil, not only for chemical but for 
biological reasons as well. By it the organic matter that 
would soon accumulate to the exclusion of higher plant life is 
disposed of, and its nutrient materials are brought into a 
condition in which they may be absorbed by roots. The 
presence of oxygen is essential either directly or indirectly 
to the organisms that facilitate decomposition. Through such 
a process, roots of past crops, as well as other organic matter 
that has been plowed under, are rapidly changed in the soil. 
The processes of decay give rise to products, chiefly carbon 
dioxide, that are solvents of mineral matter, and leave the 
nitrogen and ash constituents more or less available for plant 
use. 

Oxygen is also necessary for the germination of seeds and 
the growth of roots. These phenomena, although not involv- 
ing the removal of large quantities of oxygen, are entirely de- 
pendent on its presence in considerable amounts. 

134. Volum^e of the soil air. — The amount of air in soils 
is determined by their physical properties, the variability in 
any particular soil being due to certain changes to which such 
a soil is normally subject from time to time. The factors 
that influence the volume of air in soil are: (1) texture; (2) 
structure; (3) organic matter; and (4) moisture content. 

It is a well recognized fact that the finer the texture, the 

better the granulation and the larger the amount of organic 

matter, the greater is the amount of pore space. Since about 

the same proportion of the pore space is filled with water in 

every soil when it is in optimum condition for crop growth, 

it is obvious that with finer texture, better granulation and 

increased organic matter, there will be a greater amount of 

air present. 

Russell, E. J., and Appleyard, A., The Influence of Soil Conditions 
on the Decomposition of Organic Matter in the Soil; Jour. Agr. Sci., 
Vol. VIII, Part 3, pp. .385-417, 1917. 



258 NATURE AND PROPERTIES OF SOILS 

It must also follow that the larger the proportion of the 
interstitial space filled with water, the smaller will be the 
quantity of air contained. This does not mean that the soil 
with the higher percentage of water will contain the least air. 
The percentage pore space, which is determined by the tex- 
ture, structure, and organic matter is a consideration also. 
These three factors, together with moisture content, are in- 
volved in the following formula for calculating air space: 

% Air Space — % Pore Space — {%B.,0 X Vol. Wt.) 

If one soil, containing 30 per cent, of water, has a pore 
space of 50 per cent, and a volume weight of 1.3, its air space 
would be 11 per cent, of the total soil volume. Another soil 
with 20 per cent, of moisture, a pore space of 40 per cent, 
and a volume weight of 1.6 would, on the other hand, con- 
tain only 8 per cent, of air. The above formula, however, 
is irremediably inaccurate in two respects. It does not allow 
for the air dissolved in the soil-moisture nor does it compen- 
sate for the influence of the gelatinous colloidal material that 
exists in the interstices especially of a heavy soil. 

135. Movement of soil air. — There seems to be a slow 
but constant movement of air through the interstitial spaces 
of a normal soil in an attempt to create a homogeneous com- 
position within the soil as well as to establish equilibrium with 
the atmospheric air. The major controls of such movement 
are (1) moisture and (2) temperature changes. The minor 
influences are (1) diffusion and (2) fluctuations in atmo- 
spheric pressure. 

As water, when present in a soil, occupies certain of the 
interstitial spaces, it decreases the air space when it enters 
the soil and increases it when it leaves. The downward move- 
ment of rain-water produces a movement of soil air by forcing 
it out through the drainage channels below, while at the same 
time a fresh supply of air is drawn in behind the wave of 
saturation as the water passes down from the surface. The 



SOIL AIR 



259 



movement thus occasioned extends to a depth where the soil 
becomes permanently saturated with water. Twenty-five per 
cent, of the air in a soil may be driven out by normal change 
in moisture content. Capillary movement, whether it be pro- 
duced by evaporation, plant action or other normal forces, 
likewise produces movement of the soil air. In fact, every 
readjustment of soil-moisture, however slight, will produce 
a corresponding adjustment of the air films. 

It is generally considered that the effect of normal tempera- 
ture change on the contraction or expansion of the soil air is 
so slight as to produce but little movement. Ramann says,^ 
"Since the coefficient of expansion of gas is only 1/273 to a 
degree Centigrade and since the temperature fluctuations to 
the depths of from four to eight inches are small, the diurnal 
exchange of gas is consequently slight. ' ' Bouyoucos,^ by rais- 
ing the temperature of both dry and moist soil held in a 
properly controlled apparatus, was able to measure the 
amount of air actually expelled. He found in every case that 
the gases driven off markedly exceeded the theoretical 
amounts. 

Table LVI 
effect of temperature on the amount of air expelled from 

moist soils 



Soil 


Per 

Cent 
Mois- 
ture 


Per 

Cent 
Po- 
rosity 


Cubic Centimeters of Air Expelled 
From One-half Cubic Foot of Soil 


Theo- 
retical 
In- 




0-10°C 


10°-20°C 


20°-30°C 


30°-40°C 


FOR 

Each 
10°C 


Sandy loam 
Silt loam. . 

Clay 

Peat 


11.0 
18.6 
25.3 
92.0 


48.2 
47.0 
50.3 
38.6 


289 
326 
363 
466 


354 
335 

382 
512 


382 
428 
428 
559 


419 
465 
503 
657 


250 
244 
261 
200 



^Ramann, E., Bodenlunde, Seite 386; Berlin, 1905. 

^Bouyoucos, G. J., Effect of Temperature on Some of the Most 
Important Physical Processes m Soils; Mich. Agr. Exp. Sta., Tech. Bui. 
22, pp. 50-62, 1915. 



260 NATURE AND PROPERTIES OF SOILS 

Not only are the amounts of air expelled larger than the 
theoretical figures, but the differences rise with the tempera- 
ture. With a change of 40° C. it is to be expected that the 
actual gas expelled will exceed the theoretical from 1.2 to 2.7 
times, depending on the soil and its condition. This apparent 
discrepancy is due to the expansion of the aqueous vapor in 
the soil air and to the liberation of absorbed gases with a rise 
in temperature. 

Diurnal fluctuations in temperature often rise as high as 
15° C. for the upper six inches of soil in the summer months.^ 
When it is remembered that monthly and seasonal differences 
are even greater than the diurnal and that this respiring effect 
continues day after day, the importance of temperature in 
relation to air movement cannot be minimized. If a six-inch 
layer of soil is raised from 5° C. to 20° C. in temperature, 
about 10 per cent, of its atmosphere will be expelled, pro- 
viding the actual expansion is twice the theoretical. 

The wide difference in the compositions of soil and atmo- 
spheric gases give rise to diffusion movements, especially of 
the oxygen and carbon dioxide. This tendency towards equi- 
librium is also important in the readjustments within the soil. 
As oxidation and carbon dioxide production do not occur 
equally in all parts of the soil, diffussion movements might 
easily be induced. The readjustments and equalizations be- 
tween the soil air proper and that absorbed by the soil-mois- 
ture are probably largely diffusive. Although diffusion phe- 
nomena are slow, Buckingham- considers them quite impor- 
tant. 

Waves of high or low atmospheric pressure, frequently in- 
volving a change of 0.5 inch on the mercury gauge, are con- 
stantly following each other eastward across the continent. 
Low pressure allows the soil air to expand and issue from 

' See Swezey, G. D., Soil Temperature at Lincoln, NehrasJca; Nebr. 
Agr. Exp. Sta., 16th Aim. Eep., pp. 95-102, 1903. 

^ Buckingham, E., Contributions to Our Knowledge of Aeration of 
Soils; U. S. Dept. Agr., Bur. Soils, Bui. 25, 1904. 



SOIL AIR 261 

the soil, while a high pressure following causes the outside 
air to enter. An appreciable, but not important, movement 
of soil air is produced in this way. Gusts of wind, by affect- 
ing the air pressure, would function in the same way but 
presumably would influence only the superficial air spaces. 

136. Practical modification of soil air. — The ordinary 
operations of tillage greatly influence the ventilation of the 
soil. When a soil is plowed, the bottom of the furrow is ex- 
posed directly to the air, and, by the separation of adhering 
particles and aggregates of particles, air is brought into con- 
tact with portions that previously have been shut off from 
atmospheric influence. It is partly because of its effect on 
soil ventilation that plowing is beneficial. The necessity for 
its practice is obviously greater in a humid region and on a 
heavy soil than in a region of light rainfall and on a light 
soil. The practice of listing corn in semi-arid regions, by 
which the soil is sometimes left unplowed for a number of 
years, would fail utterly on the heavy soils of a humid region. 

Subsoiling, by loosening the subsoil, increases the ventila- 
tion at the lower depths. Rolling and subsurface packing 
both diminish the volume and the movement of air. Their 
essential difference is in their effect on moisture rather than 
on air. Harrowing and cultivation have the opposite effect, 
and both may under certain conditions increase the produc- 
tion of nitrates in the soil by promoting aeration. 

Farm manures, lime, and other amendments that improve 
the structure of the soil have for that reason a beneficial 
action on soil aeration. By their effect on the physical con- 
dition of the soil, they increase its permeability, and by stim- 
ulating oxidation and carbon dioxide production they induce 
diffusion. 

Under-drainage, by lowering the water-table and removing 
the soil-water from the larger capillary spaces, markedly in- 
fluences the aeration of the soil and thus profoundly modifies 
the chemical and biological activities therein. There is a 



262 NATURE AND PROPERTIES OF SOILS 

very considerable movement of air in and out of tile drains, 
which cannot fail to influence the aeration of the soil above. 
The influence of irrigation on the soil is much like that of 
rainfall. The alternate filling and emptying of the interstitial 
spaces with water causes a very considerable change of air. 

The roots of plants left in a soil after the crop has been 
harvested decay and leave channels in the soil through which 
air penetrates. Below the furrow slice, where the soil is not 
stirred and where it is usually more dense than at the surface, 
this affords an important means of aeration. The absorption 
of moisture from the soil by roots also causes the air to pene- 
trate, in order to replace the water withdrawn. 

137. Resume. — The air of the soil differs from the atmos- 
pheric air in being relatively lower in oxygen and compara- 
tively very much higher in carbon dioxide. It is generally 
saturated with water-vapor. The percentage of nitrogen and 
other gases is about the same as in the atmosphere. The 
major portion of the soil atmosphere exists in the larger inter- 
stices. Its movement in most cases is due to moisture and 
temperature changes, although diffusion and fluctuations in 
barometric pressure are of some importance. A minor portion 
of the soil air is dissolved in the soil-water, the absorptive 
influences of the soil complexes probably playing a part also. 
Carbon dioxide is the predominating gas in the minor por- 
tion, which maintains an equilibrium with the more active 
soil air largely by diffusion. 

While the amount of air in the soil varies with the texture, 
structure, and organic matter, the moisture content seems to 
be the dominant factor with volume as well as with movement. 
Although plowing, tillage, and manuring profoundly influence 
the soil air and its relationships to normal chemical and bio- 
logical reactions, natural forces and processes, once the crop 
is on the soil, seem to control aeration. 



CHAPTER XIII 
THE ABSORPTIVE PROPERTIES OF SOILS ^ 

It has been known from very early times that soils were 
able to take up and tenaciously hold such materials as salts 
and dyes. Aristotle, for example, noticed that sea water was 
purified when passed through sand. This capacity of soil 
to absorb and fix, more or less completely, materials added 
to it is called absorption. The earliest quantitative experi- 
ments were made by H. S. Thompson in England. He found 
that the soil was able to absorb considerable quantities of 
ammonia from ammonium sulfate, the acid radical being 
liberated. The importance of absorption phenomena has since 
attracted much attention, both from the practical and the 
theoretical standpoint.- 

138. Types of absorption. — Two general types of absorp- 
tion are usually recognized, physicaP and chemical. In the 
former case the absorbed material is supposed to be concen- 
trated on the surfaces of the absorbing substance, no chemical 
reaction taking place. The absorptive capacity of charcoal 
and cotton for dyes is a good example of such a phenomenon. 
In many cases, however, absorption is due to chemical reac- 

^ The literature on absorption by soils is so complicated and contra- 
dictory that only those concepts which are more or less definitely estab- 
lished and which have a practical bearing on soil management will be 
considered. 

^ A good review of literature will be found as follows : 

Patten, H. E., and Waggaman, W. H., Absorption by Soils; U. S. 
Dept. Agr., Bur. Soils, Bui. 52, 1908. 

Preseott, J. A., The Phenomenon of Absorption in its Eelation to 
Soils; Jour. Agr. Sci., Vol. VIII, No. 1, pp. 111-130, Sept., 1916. 

'Physical absorption is sometimes spoken of as adsorption. The ten- 
dency at present is toward the elimination of this term. 

263 



264 NATURE AND PROPERTIES OF SOILS 

tion. The tenacity with which soils absorb and hold phos- 
phoric acid is probably due to the change that the soluble 
form undergoes almost immediately in the soil/ producing 
the sparingly soluble tri-calcium phosphate (Ca3(P04)2) or 
the practically insoluble iron and aluminum phosphates 
(FePO, and AlPOJ. 

While it is generally considered that most of the material 
absorbed by soil, whether the action is chemical or physical, 
is concentrated at the surfaces of the solid material, there is 
some evidence that part of it penetrates, forming a solid solu- 
tion. For example, the longer a gas is held at high pressure 
within an absorbing material, the less will be released when 
the pressure is lowered. Again, while most absorption is 
almost instantaneous, the final equilibrium is very slow. Such 
phenomena have given rise to a theory of molecular invasion. 

In the soil it is impossible to know whether the absorption 
of any material has been purely physical, purely chemical, or 
due to both actions. In all probability both types of fixation 
occur. When a potassium compound is added to a soil, the 
potassium is taken up very readily. The fixation at first is 
probably physical. This type of absorption generates chem- 
ical reactions catalytically and the remainder, and possibly 
the greater proportion of the fixation, is probably chemical 
in nature. 

139. Causes of absorption. — Way^ was the first to ad- 
vance any definite explanation of absorption. After study- 
ing the absorptive capacity of double silicates of sodium and 
aluminum, he decided that the phenomenon was purely chem- 

^CaH,(P0,)2 -f- 2CaH2(C03)2 = Ca.i'PO,), + 4H„0 + 400^ 
Soluble Insoluble 

^Way, J. T., On the Toxver of Soils to Absorb Manure; Jour. Eoy. 
Agr. Soc, England, Vol. 11, pp. 313-379, 1850. Also, On the Power of 
Soils to Absorb Manure; Jour. Roy. Agr. Soc, England, Vol. 13, pp. 
123-143, 1852. Also, On the Influence of Lime on the "Absorptive 
Properties" of Soils; Jour. Eoy. Agr. Soc, England, Vol. 15, pp. 491- 
515, 1854. 



THE ABSORPTIVE PROPERTIES OP SOILS 265 

ieal. Wariiio'ton ' also believed in the eliemical hypothesis. 
Liebig, however, regarded absorption as largely physical. Van 
Bammelen- was the first to direct attention to the importance 
of both organic and inorganic colloidal matter to absorption 
phenomena. Tliis type of explanation seems the most plau- 
sible in light of present knowledge of the colloidal state of cer- 
tain soil constituents and from the fact that a soil very often 
does not remove different bases in chemically equivalent 
amounts.^ The fact that a soil apparently saturated with one 
base is able to absorb quantities of another is additional argu- 
ment against a purely chemical explanation. 

In the soil, especially if it is of a clayey nature, there always 
exist certain quantities of hydrated aluminum silicates of 
indefinite chemical constitution. They are generally colloidal 
in nature.* Such materials, as well as those of an organic 
character, possess high absorptive capacities, not only be- 
cause of their tremendous surface exposures but also because 
of their tendency to react quickly and easily with substances 
in the soil solution. According to Van Bemmelen, who made 

'Warington, R., On the Part TaTcen by Oxide of Iron and Alumina 
in Absorptive Action of Soils; Jour. Chem. Soc, (London), Vol. 6, 
pp. 1-19, 1868. 

^ Van Bemmelen, J. M., Die Absorptionsverbindungen und das Absorp- 
tionsvermogen der Ackercrde ; Landw. Vers. Stat., Band 35, Seite 75, 
1888. Also, Die Absorption, Dresden, 1910. 

' The uncertainty regarding the real explanation of absorption is 
shown by the controversy of Weigner, who holds to the colloidal theory, 
with Gans, who believes the phenomenon is chemical. 

Weigner, G., The Chemical or Physical Nature of Colloidal Aluminum 
Silicates Containing Water; Centrbl. f. Min. u. Palaontol., No. 9, pp. 
262-272, 1914. 

Gans, E., Concerning the Chemical or Physical Nature of Colloidal 
Water-containing Aluminum Silicates; Centrbl. f. Min. u. Palaontol., 
No. 22, pp. 699-712; No. 23, pp. 728-741, 1914. 

■* The absorptive capacity ol the soil is often ascribed to zeolites. 
The presence of zeolites in the soil, however, is extremely improbable. 
Water and the absence of oxidizing agents are essential for their for- 
mation. They are products of hydrometamorphism and not of weather- 
ing. It seems probable that the processes of weathering are not only 
opposed to zeolite formation but would destroy those already present. 

Merrill, G. P., Weathering of Micaceous Gneiss; Bui. Geol. Soc. Amer., 
Vol. 8, pp. 162-166, 1879. 



266 NATURE AND PROPERTIES OF SOILS 

a very exhaustive study of the subject, the following colloidal 
materials may function in the soil : 

1. Partially decayed remains of plant and animal tissue. 

2. Colloidal iron, aluminum, and silica. 

3. Colloidal silicates formed through weathering. 

Van Bemmelen also credits crystalline silicates with some 
absorptive power, but he does not consider such action par- 
ticularly important. 

The combinations produced by absorption are often weak, 
it being possible to leach out the substances held in the water 
of the colloidal gels. The following example of one kind of 
absorption is given by Van Bemmelen ^ and shows how com- 
plex the phenomenon may become : ten grams of a hydrogel 
having the composition SiOo.4.2 HgO, shaken with 100 cubic 
centimenter solution of 20 molecular equivalent KCl, absorbed 
0.8 to 1.1 molecular equivalent of the dissolved substance. 
The absorption in this case was as if the solution had been 
diluted with 4.2 to ,5.8 centimeters of water. As the amount 
of gel water in 10 grams of hydrogel of SiOo is about 5 cubic 
centimeters, the assumption may be made that the dissolved 
substance is taken up in equal concentration by the gel water. 
Ten grams of hydrogel of SiOg shaken with 100 cubic centi- 
meter solution of 50 molecular equivalent KCl — that is, two 
and a half times the concentration of the former solution — 
absorbs two and a half times as much, or 2.1 to 2.5 molecular 
equivalent. This applies also to concentrations five times 
stronger than the first mentioned above, but beyond that the 
relation is not so simple. It serves, however, to illustrate 
the manner in which the absorption takes place from dilute 
solutions. 

140. The absorptive capacity of soils.- — The absorptive 

*VaiL Bemmelen, J. M., Die Absorptionsverbindungen und das Ab- 
sorptionsvermogen der AcTcererde ; Landw. Vers. Stat., Band 35, Seite 
75, 1888. 

*A few important citations are as follows: 

Peters, E., tJeber die Absorption von Kali durch AcTcererde ; Landw. 
Ver. Stat, Bd. 2, Seite 113-151, 1860. 



THE ABSORPTIVE PROPERTIES OF SOILS 267 

capacity of any particular soil for gases, water, or salts in 
solution, under any particular condition, depends on the tex- 
ture of the soil and on the time during which the action is 
allowed to continue. The absorptive power of a soil may be 
determined by percolating a solution of known strength 
through a column of the soil or by shaking the sample with 
a definite amount of the solution. The following data from 
Parker ^ were obtained by shaking a 35-gram portion of soil 
for two days with a solution carrying the equivalent of about 
6.5 grams of KCl : 

Table LVII 
effect of texture on the absorption of potassium. 



Soil Type 


Potassium Absorbed 
etxpressed as milligrams 
OF KCl. 


Cecil clay 


325 


Decatur clay loam 

Carrington loam 


240 
225 


Norfolk sandy loam 


148 







Sullivan, E. C, The Interaction Between Minerals and Water Solu- 
tions; U. S. Geol. Survey, Bui. 312, 1907. 

Morse, F. W., and Curry, B. E., Reactions Between Manurial Salts and 
Clay, Mucks and Soils; N. H. Agr. Exp. Sta., 29th Ann. Rep., pp. 271- 
293, 1908. 

Deniolon, A., and Bronet, G., Sur la Penetration des Engrais Solubles 
dans les Sols; Ann. Agron., Tome 28, pp. 401-418, 1911. 

Bogue, R. H., Absorption of Potassium and PlwspJwrus Ions by 
Typical Soils; Jour. Phys. Chem., Vol. 19, No. 8, pp. 66.5-695, 1915. 

MeCall, A. G., Hildebrandt, F. M., and Johnston, E. S., The Ab- 
sorption of Potassium by the Soil; Jour. Phys. Chem., Vol. 20, No. 1, 
pp. 51-63, 1916. 

McBeth, J. G., Fixation of Ammonia in Soils; Jour. Agr. Res., 
Vol. IX, No. 5, pp. 141-155, 1917. 

Wyckoff, M. I., Absorption of Ammonium Sulfate by Soils and Quartz 
Sand; Soil Sci., Vol. Ill, No. 6, pp. 561-564, 1917. 

Kelley, W. P., and Cummins, A. B., Chemical Effect of Salts on 
Soils; Soil Sci., Vol. XI, No. 2, pp. 139-159, Feb., 1921. 

^Parker, E. G., Selective ATJsorption by Soils; Jour. Agr. Res., Vol. 1, 
No. 5, pp. 179-188, Dec, 1913. 



268 



NATURE AND PROPERTIES OF SOILS 



It is noticeable that the absorption increases with the fine- 
ness of the texture, indicating that the heavier the soil, the 
greater is the amount of material present that possesses marked 
capacity for fixation. Organic matter, in general, does not 
seem as efficacious as mineral material in absorptive reac- 
tions, especially those involving salts. 





m. 








cu^ 


^ 


600 






X 








ji/70 


/ 






ci^ 


i£^^ 


— ' 


-^oo/ 


/ 




^ 


j^N2X 


joi}:^ 


■ 


^ 















200 



400 



€00 



SOO 



WOO 



7?00 C.C. 



Fig. 49. — Curves showing the absorption of K in parts per million by 
various soils from a solution containing 200 parts to the million of 
K. The volume of the percolate is used as the abscissas. 



The influence of time on absorption is shown by the follow- 
ing data from Schreiner and Failyer.^ In this case 100 gram 
portions of soil were treated with 500 c.c. of a mono-calcium 
phosphate solution carrying 100 parts per million of PO4. The 

^Schreiner, O., and Failyer, G. H., Tlie Absorption of Phosphates 
and Potassium by Soils; U. S. Dept. Agr., Bur. Soils, Bui. 32, p. 9, 
1906. 



THE ABSORPTIVE PROPERTIES OF SOILS 2G9 

parts per million of PO4 absorbed after certain intervals of 
time are given below. (See also Fig. 49) : ^ 

Table LVIII 

effect of time and texture on the absorption of po.i from 

A SOLUTION OF CaH4(P04)2. 





Time 


PO4 Absorbed in Parts 
Per Million 




Clayey 
Soil 


Fine Sandy 
Soil 


3 minutes 


400 
410 
415 
435 
440 
445 




235 


40 minutes 


255 


1 hour 


260 


2 hours 


315 


4 hours 


335 


24 hoars 


370 







It must not be inferred that, when a solution is brought 
in contact with a soil, it always becomes weaker because of 
absorption. Negative absorption may occur in which the sol- 
vent is taken up more rapidly than the solute. Concentra- 
tion is thus induced. 

141. Selective absorption.^ — The fixation phenomena by 
the soil, whether physical or chemical, is of two types: (1) the 
absorption of molecules, the compound being taken up un- 
changed; and (2) the absorption of ions. In the first case, 

* The law which appears to govern absorption of phosphates and 
potash by the soil may be expressed mathematically as follows: 

|f=K(A-Y) 

in which K is a constant, A the maximum quantity possible for the soil 
to absorb and y the quantity actually fixed when v, volume of the 
solution, has percolated through. A short discussion of the mathematics 
of this law may be found in the following publication: Schreiner, O., 
and Failyer, G. H., The Absorption of Phosphates and Potassium by 
Soils; U. S. Dept. Agr., Bur. Soils, Bui. 32, pp. 23-24, 37-39, 1906. 

^ A very good discussion of selective absorption is found in the 
following: Parker, E. G., Selective Absorption by Soils; Jour. Agr. 
Ees., Vol. 1, No. 5, pp. 179-188, 1913. 



270 NATURE AND PROPERTIES OF SOILS 

if a residue is left, it is unchanged except in concentration. 
Such would be the case in the absorption of certain dyes, of 
gases and of hydroxides of various kinds, where the molecule 
is fixed intact. This first form of absorption is by no means 
as important as the selective absorption of ions. 

Certain compounds, called electrolytes,^ tend when in solu- 
tion to ionize or split up into ions. Thus potassium nitrate, 
a neutral salt, breaks up into K+ and N0~3 ions, the degree 
of ionization depending on the concentration of the solution. 
When such a solution is brought into contact with soil, the 
latter usually, but not always, exerts a greater affinity for the 
basic ion, leaving an excess of the acid radical in solution. 
The water present furnishes small amounts of H"^ and OH" 
ions, thereby encouraging the formation of KOH, which is 
absorbed intact, together with the K+ and OH" ions. This 
action, therefore, leaves the H^ and NO"^ ions preponderant in 
the solution, which is of necessity acid in reaction due to the 
hydrogen ion concentration. This selective absorption may be 
demonstrated with any neutral salt and any neutral absorbent, 
the resultant extract always being acid due to the selective 
absorption of the basic ions. 

142. Substitution of bases.- — Associated with the selec- 
tive absorption of bases from solution there is a liberation of 

* According to the theory of the electrolytic-dissociation or ioniza- 
tion, many compounds under certain conditions break up into electrically 
charged portions called ions. Ions may be single atoms or a group of 
atoms. Many inorganic substances are almost completely ionized. A 
few organic compounds exhibit marked dissociation but many are not 
appreciably affected. 

Water dissociates into H+ and OH- ions to the extent of about .00001 
of a per cent, or 1 part in 10,000,000. An acid yields hydrogen ions 
and other ions carrying the remainder of the molecules. Alkalies give 
hydroxyl ions and other ions consisting of the remaining portion of the 
molecules. The acidity or alkalinity of a solution is determined by its 
hydrogen-ion concentration. 

^Van Bemmelen, J. M., Das Ahsorptionsvermogen der Ackcrerde; 
Landw. Vers. Stat, Band 21, Seite 135-191, 1877. 

Sullivan, E. C, The Interaction between Minerals and Water Solu- 
tions; U. S. Geol. Survey, Bui. 312, 1907. 

Wiegner, G., Zum Basenaustausch in der Ackererde; Jour. Landw., 
Band 60, Seite 111-150. 197-222. 1912. 



THE ABSORPTIVE PROPERTIES OF SOILS 271 



other bases from the soil, which appear in the filtrate as ions 
and in combination with acid radicals. Such phenomena may 
be considered as mere basic exchange, pushed forward by the 
mass action of the ion absorbed, and is called substitution of 
bases. The change may be illustrated as follows : 
KCl 4- X„ Silicate :^ X„C1 + K Silicate 

It is unlikely that this reaction actually takes place to any 
extent in fertilizer practice.^ It is more probable that the 
acid produced by the selective absorption liberates the bases 
from their loose union with the hydrated aluminum silicate 
complexes. 

HCl + Xn Silicates ?:± XnCl + H Silicates 

A dilute solution of potassium chloride filtered through a 
soil will produce a filtrate containing some calcium, mag- 
nesium, or chloride or all of these salts and some potassium 
chloride. The more dilute the solution, the larger will be the 
proportion retained, but the less the total quantity absorbed. 
Peters - treated 100 grams of soil with 250 cubic centimeters 
of a solution of potassium salts, and found that the potassium 
of separate salts was retained in different proportions, and 
that the more concentrated solutions lost relatively less than 
the weaker ones, although more actual potassium was re- 
moved from the former. 

Table LIX 



Solution 


Grams of KjO 
Absorbed From a 
1/10 Normal Solu- 
tion 


Grams op K^O 
Absorbed From a 
1/20 Normal Solu- 
tion 


KCl 

KoSO^ 


.3124 
.3362 
.5747 


.1990 

.2098 


K0CO3 


.3134 







^Parker, E. G., Selective Absorptian hy Soils; Jour. Agr. Res., Vol. 1, 
No. 5, p. 180, 1913. 

^Peters, E., rber die Absorption von Kali durch Ackererde; Landw. 
Vers. Stat, Band 2, Seite 113-151, 1860. 



272 NATURE AND PROPERTIES OF SOILS 

The same bases are not always absorbed in the same propor- 
tion by different soils; one soil may have a greater absorp- 
tive power for potassium, while another may retain relatively 
more ammonia. They seem to be somewhat interchangeable, 
as any absorbed base may be released by a number of others 
in solution. The absorptive power of a soil for certain bases 
is reflected in the composition of the drainage water from the 
soil. The latter varies with the soil, and a soluble fertilizer 
applied to one soil will have a different effect on the composi- 
tion of drainage water than if applied to another soil. This 
is well illustrated from lysimeter experiments by Gerlach ^ 
at Bromberg. Several soils were used, a portion of each being 
fertilized and unfertilized respectively. The lysimeters were 
1.2 meters deep and contained 4 cubic meters of soil. The 
drainage water was collected and analyzed for four years. 
The first yeai there was no crop, the second year potatoes were 
grown, the third oats, and the fourth rye. The following re- 
sults were obtained : 

Table liX 

AVERAGE COMPETITION OP DRAINAGE WATER IN PARTS PER MIL- 
LION. BROMBERG. 











Or- 






Soil 


Treatment 


Total 

N 


NO3 


ganic 

N 


K2O 


CaO 


Moor soil 


Fertilized 


32.7 


30.0 


2.7 


32.2 


405 




Untreated 


65.0 


60.3 


4.7 


26.2 


507 


Sand low in or- 














ganic matter. . . 


Fertilized 


25.5 


25.1 


.4 


25.1 


92 




Untreated 


20.9 


20.4 


.5 


8.5 


90 


Sandy loam high 














m organic 














matter 


Fertilized 


67.8 


64.6 


3.1 


70.2 


399 




Untreated 


69.5 


66.1 


3.4 


47.4 


414 



^ Gerlach, U., tJher die durch sicl'crwasser dem Boden Entzogenen 
Menge Wasser und Nahrstoffe; 111. Landw. Zeitung, 30 Jahrgrange, Heft 
95, Seite 871-881, 1910. 



THE ABSORPTIVE PROPERTIES OF SOILS 273 

143. Importance of absorption. — Absorption is impor- 
tant, not only because it allows the soil to retain certain nutri- 
ents against excessive leaching, but because it facilitates the 
condensation and concentration of gases within the soil.^ Rus- 
sell and Appleyard - have shown that the inner soil air is 
held very tightly and must in consequence be under consid- 
erable pressure. Such gas absorption tends to force reactions 
which otherwise would be very slow. A part of the catalytic 
power of the soil may be accounted for in this way. Moreover, 
the absorption of water by the soil is by no means unimportant. 
It is because of such phenomena that the moisture of the soil 
occurs in various forms and possesses distinctly different re- 
lationships to the plant. 

The selective absorption of the basic ions by soils of every 
type is important in a number of ways. In the first place, 
potassium, calcium, magnesium, and iron function in the soil 
as bases. Selective absorption tends to conserve these nutri- 
ents to the exclusion of their acid radicals, which are readily 
lost in drainage. Phosphorus, however, has a different status, 
for although it is held as a part of an acid radical (PO4), it is 
saved from leaching by the insolubility of the compounds 
which tend to form. In the second place, selective absorption 
apparently produces residues w^hen fertilizers are added and 
these residues are almost always acid. Sodium nitrate, am- 
monium sulphate, potassium chloride, and potassium sulphate 
will leave an acid residue in the soil solution unless influenced 
by extraneous factors, such as the addition of lime or the ac- 
tion of plants. 

^Patten, H. E., and Gallagher, F. E,, Absorption of Vapors and Gases 
by Soils; U. S. Dept. Agr., Bur. Soils, Bui. 51, 1908. 

McGeorge, W., Absorption of Fertiliser Salts by Hawaiian Soils; Haw. 
Agr. Exp. Sta., Bui. 35, p. 32, 1914. 

Cook, E. C, Factors Affecting the Absorption and Distribution of 
Ammonia Applied to Soils; Soil Sci., Vol. II, No. 4, pp. 305-344, 1916. 

* Russell, E. J., and Appleyard, A., The Atmosphere of the Soil: Its 
Composition and the Causes of Variation; Jour. Agr. Sci., Vol. VII, 
Part 1, pp. 1-48, 1915. 



274 NATURE AND PROPERTIES OF SOILS 

The acidity of soils, which is a function not only of the soil 
solution but of the solid portions also, is frequently attributed 
to certain absorptive phenomena, one idea being that, due 
to physical and chemical absorption of bases, a concentra- 
tion of the hydrogen ion is produced and actual acidity re- 
sults. Basic exchange seems to liberate iron and aluminum, 
the salts of which easily hydrolize and yield acid solutions. 
If, as some investigators maintain, the toxic principle of the 
so-called acid soils is active aluminum, manganese or similar 
elements, absorption may again be the activating phenomenon, 
since an unsatisfied absorptive capacity, especially for cal- 
cium and magnesium, seems to favor the presence of such 
constituents in the soil solution. 

The absorptive power of the soil is a controlling factor as 
far as the composition and concentration of the soil solution 
is concerned. Any study of the dynamic relationships of the 
water solution that exists in the soil interstices and in the col- 
loidal complexes which coat the soil particles, must reckon 
with absorption phenomena and all of the factors which tend 
to influence them. 



CHAPTER XIV 
THE SOIL SOLUTION 

The soil is a heterogeneous mixture of solids, gases, and a 
liquid. The mineral constituents come from the debris of 
rock, the organic matter is derived from plant and animal 
tissue, while through and around these complex materials the 
water and gases of the soil circulate in ever-changing propor- 
tions. Minute organisms are also present in great numbers, 
aiding, through their enzymic activities, the intricate trans- 
formations. As a result of the reactory inter-relations of the 
soil components, a solution is generated which tends to come 
into equilibrium with the solids and gases with which it is 
in contact. As it is from this source that plants obtain their 
mineral nutrients, the soil solution and its control demand 
especial attention. 

The fundamental error of many soil conceptions has been 
to regard the soil as a static system. Chemical, physical, and 
biological activities are admitted, but they have been regarded 
as of little importance in influencing the soil mass as a whole. 
Such a conception is in error as every constituent of the soil 
is dynamic. The presence of large amounts of material in 
a colloidal state makes the constancy of any particular con- 
dition impossible over any extended period. 

In studying the soil solution, especially as to its composi- 
tion and concentration, the phenomenon of absorption can 
not be ignored. The tendency of certain portions of the soil 
to go into solution, while other parts are absorbing both the 
solvent and the solute, must be reckoned with. Moreover, 
the losses of nutrients to the plant and through leaching are 

275 



276 NATURE AND PROPERTIES OF SOILS 

a factor to be considered. Obviously the concentration and 
composition of the soil solution is first of all a function of 
the absorptive capacity of the soil complexes, modified by the 
rate of solution and the magnitude of crop and leaching 
activities. 

144. Absorption and the soil solution. — In a bare moist 
soil, where there is no evaporation or leaching to disturb 
equilibrium ' tendencies, the soil presents a three-phase 
system. The phases are: (1) the solution surfaces,^ 
(2) the absorptive or colloidal surfaces, and (3) the 



SOLUTION 
SURFACES 



ABSORPTfOM 
COMPLEXES 




SOIL 
SOLUTION 



Fig. 50. — Diagram showing the equilibrium tendencies that exist between 
the solution surfaces, the colloidal complexes and the soil solution. 



soil solution itself. When solution takes place, the con- 
stituents so affected are acquired in part by the soil mois- 
ture as a solute and in part by the absorptive complexes. 
There is a constant attempt at equilibrium, which of course 
is never attained as long as solution continues. Under field 
conditions, many other disturbing factors enter. The rate 
of solution may vary, and the capacity and character of the 
absorbing colloidal complexes are always changing. Moreover, 
the amount of water in the soil is never constant, due to 
drainage and evaporation. The feeding of the plant, as re- 

^ This term refers to the soil surfaces from which solution takes 
place. 



THE SOIL SOLUTION 277 

gards both water and nutrients, and losses by leaching, must 
always be considered. In addition, the effect of tillage as 
well as the common practices of adding farm manure, plow- 
ing under of green-crops and applying fertilizers and lime, 
are constantly effective in obstructing equilibrium adjust- 
ments.^ (See Fig. 50.) 

The soil solution is, therefore, markedly dynamic in char- 
acter, constantly changing in composition and concentra- 
tion. Its important control is absorption, the absorptive sur- 
faces acting as a depository, in which active reserve nutrients 
are held. As the solution is depleted in any constituent, 
quicker adjustment takes place between the solvent and the 
colloidal complexes than is possible between the solution and 
the solution surfaces. Rapid adjustments, as far as the sup- 
ply of nutrients for plants is concerned, is possible only be- 
cause of the absorptive properties of the colloidal complexes 
of the soil. 

145. Methods of studying the soil solution. — Questions 
regarding the soil solution are difficult to answer because no 
adequate procedure has been devised for extracting a repre- 
sentative sample of the solution as it existed in the soil. More- 
over, no wholly satisfactory method has been perfected for 
its measurement in place. Various extractive methods have 
been tried. Briggs and McLane ^ attempted to sample the 
solution by the use of a centrifuge developing a force of two 
or three thousand times that of gravitation. When the soil 
contained a rather large quantity of capillary water, a small 
amount of it could be removed in this way. 

* Bouyoueos has shown that even under controlled conditions the 
equilibrium between finely ground minerals and water is not absolute 
or real due to the complex hydration and hydrolysis which continually 
occur. Bouyoueos, Gr. J., Eate and Extent of Solubility of Minerals 
and Eocks under Different Treatments and Conditions; Mich. Agr. Exp. 
Sta., Tech. Bui. 50, July, 921. 

* Briggs, Lyman J., and McLane, John W., The Moisture Equivalent of 
Soils; U. S. Dept. Agr., Bur. Soils, Bui. 45, pp. 6-8, 1907. 



278 NATURE AND PROPERTIES OF SOILS 

Another device, perfected by Briggs and McCall/ consists 
of a close-grained, unglazed porcelain tube, closed at one end 
and provided at the other with a tubulure, by which it can 
be connected with an exhausted receiver. This tube is mois- 
tened and buried in the soil. If the moisture content of the 
soil is sufficient to reduce the pressure of the capillary water 
surface in tJie soil to less than half the difference between the 
pressure inside and outside of the tube, there will be a move- 
ment of water inward. The water may be collected and ana- 
lyzed. 

More recently Van Suchtelen has used another method to 
obtain the soil solution.^ He replaces the soil-water by means 
of paraffin in a liquid state, at the same time subjecting the 
soil on a filter to suction. The displaced water is considered 
to represent the soil solution. Later Van Suchtelen and Itano 
substituted pressure for suction, modifying the apparatus to 
meet the new procedure. This apparatus has been further 
perfected by Morgan.^ Lipman ^ has proposed a method in 
which very high pressure, a minimum of 53,000 pounds to the 
square inch, is utilized in squeezing out the soil- water. ^ 

All such methods are open to the objection that the sample 
is not representative. The soil solution changes both in eon- 

^ Briggs, Xj. J., and McCall, A. G., An Artificial Boot for Inducing 
Capillary Movement of Soil Moisture; Science, N, S., Vol. 20, pp. 
566-569, 1904. 

" Van Suchtelen, F. H. H., MetJiode zur Gewinnung der NatiirlicJien 
Bodenlosung; Jour. f. Landw., Band 60, Seite 369-370, 1912. 

^ Morgan, J. F., The Soil Solution Obtained by the Oil Pressure 
Method; Mich. Agr. Exp. Sta., Tech. Bui. 28, Oct., 1916. 

* Lipman, C. B., A New Method of Extracting the Soil Solution ; Univ. 
Cal. Pub., Agr. Sci., Vol. 3, No, 7, pp. 131-134, 1918. Eamann, E., et al., 
have proposed a similar method but with less pressure. Internat. Mit. f. 
Bodenkunde, Bd. 6, Seite 27, 1916. 

For a good criticism of this method, see Northrup, Zea, Science, 
N. S., Vol. XLVII, No. 1226, p. 638, June 1918. 

^ Ischerekov in 1907 used ethyl alcohol to displace the water in a 
soil column utilizing only the force of gravity. Parker claims that 
this method is of considerable value. He found that data so obtained 
compared closely with that obtained from the water extract method. 
Parker, F. W., Methods of Studying the Concentration of the Soil 
Solution; Soil Sci., Vol. XII, No. 3, pp. 209-232, 1921. 



THE SOIL SOLUTION 279 

centration and composition so readily that the addition of ex- 
traneous material or the exertion of unnatural pressure defeat 
the object of the determination. Moreover, the soil solution is 
probably not homogeneous and unless practically all of it is 
removed a sample of value cannot be obtained. The signifi- 
cance of such a sample, if it were attained, is questionable, 
as it is impossible to know tlie proportion of the soluble nu- 
trients that may actually be appropriated by the growing 
plant. 

The method of obtaining soil extracts has been used to a 
greater extent than any other in studying the soil solution. 
Water is the usual solvent. The Bureau of Soils filter method ^ 
is commonly followed. As might be expected, it is purely 
arbitrary in its procedure, the idea being to make the results 
comparative rather than strictly quantitative. Soil and water 
in the proportions of 1 to 5 are mixed, stirred three minutes 
and allowed to stand twenty minutes. The supernatant liquid 
is then forced through a Pasteur-Chamberland filter and a 
clear extract obtained for analysis. 

The solution obtained is not representative of the soil-water 
and its solutes. It is only an extract of the soil. The addi- 
tion of a large amount of water is a disturbing factor. The 
concentration of the extract is also modified by the absorptive 
power of the soil, being relatively greater for a sandy than 
for a clayey soil. Moreover, the differential influence of the 
solvent comes into play, for as soon as solution begins, the 
solvent is no longer pure water but a solution of constantly 
changing efficiency. Nevertheless, the work of Hoagland, 
Stewart and Burd ^ indicates that there is not only a relation- 

^ Schreiner, O., and Failyer^ G. H., Colometric, Turbidity and Titra- 
tion Methods Used in Soil Investigations ; U. S. Dept. Agr., Bur. Soils, 
Bui. 31, 1906. 

' Hoagland, D. E., The Freezing Point Method as an Index of Varia- 
tions in the Soil Solution Due to Season and Crop Growth; Jour. Agr. 
Ees., Vol. XII, No. 6, pp. 369-395, 1918. 

Stewart, G. E., Effect of Season and Crop Growth in Modifying the 
Soil Solution; Jour. Agr. Ees., Vol. XII, No. 6, pp. 311-368, 1918. 



280 NATURE AND PROPERTIES OF SOILS 

ship between the water extract of a soil and its productivity, 
but a correlation with the strength of the soil solution as well. 
The extract method is especially valuable in studying the 
nitrates of the soil solution. As nitrate nitrogen does not 
suffer as much absorption as do the nutrient bases, that which 
appears in the extract is a fair measure of the strength of the 
soil solution insofar as this constituent is concerned. 

The only method for measuring the concentration of the soil 
solution in situ is that of Bouyoucos.^ This is known as the 
depression of the freezing point method. It is possible, when 
dealing with a pure solution of a known salt, to calculate its 
concentration by determining how much the freezing point is 
lowered or depressed below 0° C. This principle is applied 
to the soil by using a Beckman thermometer and the proper 
control apparatus. As the soil solution carries a great num- 
ber of different ions in unknown proportions, it is impossible 
to calculate even the concentration with accuracy, a factor 
of somewhat doubtful validity being utilized. The procedure 
gives nothing regarding the presence of specific ions nor are 
its results uniform, due to the variable dissociation of the salts 
present. Nevertheless the method has thrown much light 
on the many difficult problems of the soil and its solution. 

146. Qualitative composition of the soil solution. — Once 
the dynamic character of the soil solution is conceded, three 
points of importance immediately demand attention: (1) the 
qualitative composition of the soil solution and its concentra- 
tion in toto, (2) the quantitative composition, and (3) the 
factors most important in influencing both the composition 
and the concentration of the solution. 

It must be recognized at the outset that the soil solution 

Burd, J. S., Water Extractions of Soils as Criteria of their Crop 
Producing Poiver; Jour. Agr. Res., Vol. XII, No. 6, pp. 297-309, 1918. 

Hoagland, D. R., Martin, J. C, and Stewart, G. R., Relation of the 
Soil Solution to the Soil Extract; Jour. Agr. Res., Vol. XX, No. 5, 
pp. 381-395, 1920. 

^ Bouyoucos, G. J., Further Studies on the Freezing Point Lowering of 
Soils; Mich. Agr. Exp. Sta., Tech. Bui. 31, Nov., 1916, 



THE SOIL SOLUTION 281 

is generally dilute except in arid regions under conditions of 
alkali. The concentration probably very seldom exceeds 30,- 
000 parts per million and is normally very much lower. More- 
over, the greater proportion of the solute is in an ionic state, 
molecules appearing only when the concentration is relatively 
high. It is well to note that the plant absorbs most of its 
nutrients in the ionic condition. 

From the knowledge obtained by the analysis of soil ex- 
tracts, it is safe to assume that all of the common bases and 
acid radicals normally occur in the soil solution. Thus, K"", 
Na% Mg^% Ca^% Fe^*\ Al+^^ and NH^+ ions may be expected 
as well as such ions as SO4, SiOf, CI", PO4, NO;, NO; and 
CO3. Since water dissociates slightlj'-, H+ and OH" ions will 
also be present. The reaction of the solution will depend on 
its hydrogen-ion concentration and may be alkaline, neutral 
or acid as the case may be. Most soil solutions seem to be 
slightly acid,^ possibly due to the action of carbon dioxide. 

Morgan ^ found on an examination of the solutions obtained 
from soils by the oil pressure method that, as the moisture in- 
creased, the concentration of the solution decreased. These 
findings are amply corroborated by the work of Bouyoucos ^ 
with the depression of the freezing point method. The latter 
presents data regarding the actual concentrations at various 
moisture contents, which seem to indicate the general differ- 
ences that may be expected between soils of different types. 

^ Gillespie, L. J., The Eeaction of Soil and Measurements of Hydro- 
gen-ion Concentration; Jour. Wash. Acad. Sci., "Vol. 6, No. 1, pp. 
7-16, 1916. 

Sharp, L. T., and Hoagland, D. E., Acidity and Adsorption in Soils 
as Measured by the Hydrogen Electrode; Jour. Agr. Res., Vol. VII, 
No. 3, pp. 123-145, 1916. 

Hoagland, D. R., delation of the Concentration and Eeaction of the 
Nutrient Medium to the Groioth and Absorption of the Plant; Jour'. 
Agr. Res., Vol. XVIII, No. 2, pp. 73-117, 1919. 

' Morgan, J. P., The Soil Solution Obtained by the Oil Pressure 
Method; Mich. Agr. Exp. Sta., Tech. Bui. 28, 1916. 

•Bouyoucos, G. J., Further Studies on the Freezing Point Lowering 
of Soils; Mich. Agr. Exp. Sta., Tech. Bui. 31, pp. 14-15, 1916. 



282 



NATURE AND PROPERTIES OF SOILS 



Table LXI 

the concentration of the solution of various soils as de- 
termined by the depression of the freezing point, ex- 
pressed in parts per million based on dry soil. 



Soil 


Moisture 
% 


CONCENTRA- 

TIOK 

P. P. M. 


Moisture 
% 


Concentra- 
tion 
p. p. M. 


Superior clay . . . 
Miami silt loam . 
Carrington loam 
Plainfield sand. 
Peat 


18.8 
8.8 

15.2 
5.0 

61.3 


29,268 
19,560 
16,390 
6,342 
23,333 


39.4 
36.0 
38.5 
24.6 
208.5 


415 
707 
463 
366 
2,222 







147. Quantitative composition of the soil solution. — 
Data regarding the relative or actual quantities of the nutri- 
ent elements in the soil solution are not only very meagre but 
unreliable. Morgan ^ found, on comparing the solutions ob- 
tained from different soils by the oil pressure method, that the 
potassium (K) might vary from 4 to 180 parts per million 
based on dry soil; the phosphorus (PO4) from .2 to 4.6, and 
the calcium (Ca) from 6 to 1000 parts per million. King,^ in 
his extensive work with soil extracts, found the nitrate nitro- 
gen (NO3) extremely variable, ranging from a fraction of a 
part per million to more than 150 parts per million in the same 
soil at different times. A greater fluctuation is to be expected, 
however, in the nitrate nitrogen than with the other elements, 
since the presence of soluble nitrogen in the soil solution is due 
very largely to biological activity. The following figures from 
Morgan, although the different samples should not be com- 
pared, show what may be expected in general regarding the 
concentration of particular elements in the soil solution. 

* Morgan, J. F., TTie Soil Solution Obtained by the Oil Pressure 
Method; Mich. Agr. Exp. Sta., Tech. Bui. 28, 1916. 

* King, F. H., Investiqations in Soil Management; U. S. Dept. Agr. 
Bur. Soils, Bui. 26, 1905. 



THE SOIL SOLUTION 



283 



Table LXII 

the amounts of potassium, phosphorus, and calcium in the 

solution op various soils as determined by the oil 

pressure method. expressed in parts per million 

based on dry soil. 





Moisture 

Per- 
centage 


Parts Per Million 


Soils 


K 


PO. 


Ca 


NH3+NO3 


Fine sandy loam. 
Medium sandy 
loam 


29.7 

27.2 

41.9 

37.8 

24.5 

132.9 


7.18 

9.82 

12.44 

27.02 

11.03 

139.33 


1.54 

1.41 

1.85 
4.64 
1.13 
2.19 


9.10 

12.75 

37.12 

25.93 

10.56 

213.70 


.91 
13.56 


Clyde fine sandy 
loam 


3.80 


Miami silt loam. . 

Miami clay 

Peat ! 


L20 

1.61 

33.91 







Morgan's data indicate that the least variation may be ex- 
pected in the phosphorus (PO4) content, which does not differ 
greatly in different soil solutions nor does it vary to any great 
extent in the same soil. Potassium (K) and especially cal- 
cium (Ca) show considerable fluctuation, as does the nitrate 
nitrogen (NO3), as has already been emphasized. The figures 
of Morgan correlate fairly well with the data obtained by the 
Bureau of Soils ^ by means of centrifugal extraction. The 
potassium (K) averaged about 28 parts per million based on 
the solution, the calcium (Ca) 32, and the phosphorus (PO4) 
8 parts per million. 

148. Influence of season and crop on the soil solution. — 
It has already been emphasized that the concentration and 
the composition of the soil solution suffer wide fluctuations. 
The principal causes of such variations are as interesting as 

* Cameron, F. K., The Soil Solution; p. 40, Easton, Pa., 1911. 



284 NATURE AND PEOPERTIES OF SOILS 

they are important since they have a bearing not only on the 
chemical and biological phenomena within the soil but also 
on its plant relationships. 

The broadest and most general factors affecting the soil 
solution are season and crop, Wliether the soil is fallow or 
covered with vegetation, a great seasonal influence is evident 
on the soil and its solution, Stewart,^ working in California 
with extracts from thirteen soils held in large containers, 
found notable fluctuations of nitrates, calcium, potassium, and 
magnesium both in bare and cropped earth. The phosphates 
did not show great variation. The soluble nutrients were 
markedly higher in the bare soils, the differences between the 
various types being quite noteworthy. The good soils seemed 
to have the more concentrated soil solution, a conclusion al- 
ready reached by a number of investigators.^ When crops 
were growing on these soils, the concentration of soluble nu- 
trients not only was lower than with the fallowed areas, but 
it was about the same in every type of soil. The inherent 
solution capacity of the different soils was roughly indicated 
by the crop growth. Hoagland's^ study of the concentration 

^Stewart, G, R., Effect of Season and Crop Growth in Modifying 
the Soil Solution; Jour. Agr. Res., Vol. XII, No. 6, pp. 311-368, 1918. 

* Snyder, H., The Water-Soluble Plant Food of Soils; Science^ N, S,, 
Vol. 19, No, 491, pp. 834-835, 1904. 

King, F. H., Investigations in Soil Management ; Madison, Wis,, 
1904. 

King, F. H., Investigations in Soil Management; U, S. Dept. Agr., 
Bur. Soils, Bui, 26, 1905, 

Mitscherlich, E. A., Ei7ie Chemische Bodenanalyse fur Pflanzen- 
physioJogische Forschungen; Landw. Jahrb., Bd. 36, Heft 2, S. 309-369, 
1907. 

Lyon, T, L., and Bizzell, J. A., The Plant as an Indicator of the 
Belative Density of the Soil Solutions; Proc. Amer. Soc. Agron., Vol. 
IV, pp. 35-49, 1912. 

Hall, A. D., Brenchley, W, E,, and Underwood, T. M., The Soil Solu- 
tion and tJie Mineral Constituents of the Soil; Philosoph, Trans. Roy, 
Soc, London, Series B, Vol, 204, pp. 179-200, 1913. 

Pantanelli, E., Bicerche Sulla Concentrasione del Liquide Circolante 
nei Terreni Libici; Bui. Orto Bot. R., Univ. Napoli, T. 4, pp. 371-383. 

^ Hoagland, D. R., The Freezing Point Method as an Index of Varia- 
tions in tlie Soil Solution Due to Season and Crop Growth; Jour. Agr, 
Res., Vol, XII, No. 6, pp. 369-395, 1918. 



THE SOIL SOLUTION 



285 



of the solution in these soils through the growing season by 
the freezing point method corroborates the conclusions drawn 
from the water extracts. The investigation also indicates that 
large amounts of nutrients are made available by cultivation, 
fallowing, and cropping and that, from the standpoint of the 
soil solution, the ordinary farm practices are inherently sound. 
Hoagland's data regarding some of the soils studied is given 
in Table LXIII. The moisture content was approximately the 
same for each soil. 

Table LXIII 

THE CONCENTRATION OF THE SOIL SOLUTION IN PARTS PER MIL- 
LION FROM A GOOD AND POOR SOIL EACH FALLOWED OR 
CROPPED TO BARLEY. 





Fertile Soil 


Poor Soil 


Date 


FALLOW 


CROPPED 


FALLOW 


CROPPED 


July 10 

July 24 

Aug. 21 

Oct. 23 

Dec. 18 

Feb. 12 

Mav 7 


2000 
1700 
1800 
4300 
3400 
4200 
6700 


1200 

500 
700 
1900 
1500 
1900 
3800 


1100 
800 
1300 
2900 
1800 
2700 
6300 


600 

200 

400 

900 

3000 

1800 

3700 







Further investigations of Hoagland with Martin ^ indicate 
that the effect of cropping on the soil solution persists for 
a considerable period. A marked relationship was also noted 
between the soil solution and the physical condition of the 
soil, due to a change in the colloidal matter with season. An 
increase in colloidal matter was noted when the soil solution 
was depleted of its solutes by plant activities. 

^Hoagland, D. E., and Martin, J. C, Elfect of Season and Crop 
Growth on the Physical State of the Soil; Jour. Agr. Kes., Vol. XX, 
No. 5, pp. 397-404, 1920. 



286 



NATUEE AND PROPERTIES OF SOILS 



149. Other factors influencing' the soil solution. — A num- 
ber of other conditions, which are really phases of season, 
influence both the concentration and the composition of the 
soil solution. Among these are temperature, leaching, and 
the moisture content of the soil. As the soil warms up in the 
spring, reactions of all kinds are stimulated and an increase 
in concentration generally results. If considerable rain-water 
enters the soil, the soil solution is much diluted. It is also 
changed in composition, due to the equilibrium adjustments 
that of necessity occur. The following data from Bouyoucos ^ 
show the influence of change in moisture on the concentra- 
tion of the soil solution : 

Table LXIV 

concentration of the solution of certain soils at various 

moisture contents. lowering of the freezing 

point method. 



Soils 


Moisture 
% 


Concen- 
tration 

p. p. M. 


Moisture 

% 


Concen- 
tration 

p. p. M. 


Sand 

Sandy loam. . . . 
Loam 


2.60 

8.30 

11.18 

17.40 

18.80 


3,939 
13,639 
13,780 
20,153 
28,940 


21.98 
21.53 
20.97 
34.76 
36.50 


303 
606 

848 


Silt loam 

Clay 


1061 
1030 







If the soil is moistened beyond its water-holding capacity, 
it is obvious that drainage losses will occur, which will deplete 
the soil of valuable constituents. Increase of moisture, there- 
fore, may modify the soil solution temporarily or permanently, 
according to conditions. 

Tillage and the addition of various materials also have a 

^Bouyoucos, G. J., The Freezing Point Method as a New Means of 
Measuring the Concentration of the Soil Solution Directly in the Soil; 
Mich. Agr. Exp. Sta., Tech. Bui. 24, 1915. 



THE SOIL SOLUTION 287 

remarkable influence on the soil solution, especially increasing 
its concentration during the warmer seasons. Plowing and 
cultivation by stimulating biological activity may enhance ni- 
trate production to a marked degree in a short time. Aeration 
will often increase the available mineral elements by the en- 
couragement of reactions which favor solution. The addition 
of salts of various kinds has been shown by Bouyoucos ^ to 
influence the soil solution profoundly. The compounds added 
afi'ected different soils in a diverse manner. When neutral 
salts were added, the soil solution was increased from 35 to 
100 per cent, of the added strength of the salts. In the case 
of phosphate salts the increase was very much less. 

150. The soil solution and productivity. — As the crop 
obtains its nutrients from the soil solution, there must be a 
direct relationship between the fertility of the soil and the con- 
centration and composition of the soil solution. The data 
quoted from Hoagland indicate in a broad way that a fertile 
soil is capable of maintaining a more concentrated soil solu- 
tion than is a poorer one. The work of other investigators 
amply corroborates this assumption.^ One rather convincing 
experiment may be quoted. 

Hall, Brenchley, and Underwood ^ analyzed the water ex- 
tract from certain plats on the Rothamsted Experiment Sta- 
tion farm, the fertilizer treatment and the yields of which 
had been recorded for a long term of years. Complete analyses 
of the soil from the several plats were also made : 

* Bouyoucos, G. J., The Freezing Point Method as a Means of Studying 
Velocity Beactions Between Soils and Chemical Agents and Behavior of 
Equilibrium; Mich. Agr. Exp. Sta., Tech. Bui. 37, 1917. 

Also, Rate and Extent of Solubility of Soils under Different Treat- 
ments and Conditions; Mich. Agr. Exp. Sta., Tech. Bui. 44, 1919. 

See also, Spurway, C. H., The Effect of Fertiliser Salt Treatments on 
the Composition of Soil Extracts; Mich. Agr. Exp. Sta., Tech. Bui. 45, 
1919. 

^See citations page 284. 

='Hall, A. D., Brenchley, W. E., and Underwood, T. M., The Soil 
Solution and the Mineral Constituents of the Soil; Phil. Trans. Koy. 
Soc, London, Series B, Vol. 204, pp. 179-200, 1913. 



288 NATURE AND PROPERTIES OF SOILS 

Table LXV 

yields to the acre op crops, and composition of soil and 

water extract of soil. rothamsted experiment 

station farm. england. 



Treatment 


Yield to 
THE Acre 


Complete Analy- 
sis 


Water Extract 




(POUNDS) 


% 


K,0 

% 


P2O. 

p. p. M. 


K2O 

p. p. M. 


Untreated 

N + K2O 


1276 

2985 
3972 
5087 
6184 


.099 
.102 
.173 
.182 
.176 


.183 
.257 
.248 
.326 
.167 


.525 

.808 
3.900 
4.025 
4.463 


3.40 
30 33 


N + PA 

N + K^O + PA-' 
Farm manure .... 


3.88 
24.03 
26.45 



151. Summary. — The solution as it exists in a normal 
soil is highly dynamic. Its concentration and composition 
are fundamentally governed by rate of solution, by absorp- 
tion, and by the amounts of the various solutes in the solution 
itself. Many factors are active in preventing a condition of 
equilibrium between these three phases. Those of especial 
importance are season and crop. Temperature, moisture con- 
tent, and leaching are subfactors of season. Tillage of all 
kinds and the addition of manures, lime, and fertilizers are 
practical means of modifying the soil solution moie to ade- 
quately meet the needs of the crop. In fact, all of the com- 
mon practices so successfully used in economic soil manage- 
ment attain their end through a modification and control of 
the soil solution. 



CHAPTER XV 

THE REMOVAL OF NUTRIENTS FROM THE SOIL BY 
CROPPING AND LEACHING 

The soil solution, because of its dynamic character, offers 
two sources of loss for nutrient materials, one of which should 
be economically encouraged, while the other should be reduced 
by suitable control to as low a point as is consistent with good 
soil management. These two sources of exhaustion are (1) 
cropping and (2) leaching or drainage. One is a legitimate 
expenditure ; the other is a waste, which within certain limits 
in a humid region is unavoidable.^ 

152. Intalce of water by plants — osmosis. — Plants ob- 
tain their raw materials from the air and the soil, the former 
furnishing the carbon and the oxygen, most of the water and 
the nutrients proper coming from the soil. Although many 
constituents, some necessary and some incidental, pass into 
the plant from the soil, for convenience of discussion two 
groups may be established: (1) water, and (2) nutrients prop- 
er. It must be kept in mind, however, that water, while per- 
forming certain mechanical functions, has a nutrient relation- 
ship also. 

The most important mechanical principle governing the ab- 
sorption of water by the plant is osmosis.'- The abstract phe- 
nomenon should be clearly in mind before its plant relation- 
ships are considered. A bag of collodion (pig's bladder or 
parchment paper will do as well) is filled with a strong solu- 

^ Gases, such as carbon dioxide, nitrogen and possibly ammonia, may 
be lost from the soil also. 

* Water may also be taken up by colloidal absorption which is called 
imbibition. This is common in seeda. 

289 



290 NATURE AND PROPERTIES OF SOILS 

tion of cane-sugar. The walls of such a bag are semi-permea- 
ble, that is, certain materials will pass through readily while 
others will pass but slowly. For example, the sugar mole- 
cules penetrate with difficulty, while the water finds the walls 
of the bag but a slight obstacle. 

If this collodion bag with its sugar solution is attached to a 
capillary tube and immersed in pure water, it at once becomes 
distended and the liquid will rise in the capillary tube, indi- 
cating an unequal pressure within the system. The pressure 
develops because of the separation of the pure water and the 
sugar solution by a membrane that is penetrated at different 
rates by the molecules and ions in contact with it. A tendency 
towards equalization of course occurs and, as the water moves 
in faster than the sugar moves out, a pressure is developed 
within the bag which becomes apparent by the rise of the 
liquid in the capillary tube. Such a phenomenon is called 
osmosis and the pressure osmotic pressure. Such force prob- 
ably has much to do with the movement of plant saps and 
fluids. Under such conditions as those maintained in the ex- 
periment, the water tends to move from the dilute solution to 
the more concentrated one. 

Suppose the collodion bag be considered as typical of the 
cells, which form the feeding surface of an active rootlet, and 
the sugar solution the relatively concentrated and partially 
colloidal cell contents. The water outside the bag will, of 
course, represent the. dilute soil solution which bathes the roots. 
With such substitutions it can readily be seen why the plant 
exerts an osmotic "pull" and how the water moves through 
the cell-wall. Such a transfer will continue until the move- 
ment of the water in the soil becomes too slow for normal 
plant activities. Wilting then occurs. (See Fig. 51.) 

In alkali soils, where the soil solution becomes very concen- 
trated, the process above described may be reversed. Out- 
ward osmosis then occurs and plasmolysis ^ may result. 

* Plasmolysis is a separation of the plasma from the cell-wall due to a 



REMOVAL OF NUTRIENTS FROM THE SOIL 291 

Bouyoucos ^ has su^jjested that the phenomena of wilting may 
be due, at least partially, to plasmolysis since he has shown 
by observing the depression of the freezing point that the soil 
solution becomes very concentrated at low moisture contents. 

Such a conception of water absorption is simple, yet it often 
leads to erroneous ideas regarding the intake of nutrients by 
plants. The amount of any particular nutrient absorbed by 
the plant is not determined by the quantity of water taken up, 
since water and nutrients enter more or less independently. 
The large amount of water imbibed by the plant, later to be 
lost by transpiration, cannot be accounted for on the basis of 
a very dilute soil solution and the necessity of rapid trans- 
piration in order to facilitate the entrance of sufficient nutrient 
substance. 

153. Absorption of nutrients by plants — diffusion. — The 
solution in a normal fertile soil is not only rather dilute 
in toto but a great proportion of the nutrients therein are in 
the ionic condition. While both molecules and ions are pre- 
sented to the absorbing surfaces of the plant, it is only the 
latter that penetrate to any great extent, although some mate- 
rials, especially those of an organic nature, do enter in a 
molecular condition. The presence of water is, of course, nec- 
essary for both ionic and molecular penetration, but only as a 
medium for diffusion. Its movement into the plant is, there- 
fore, of no very great moment in the actual diffusion process, 
as the phenomenon is called, although the approach of the 
nutrients to the feeding surfaces is considerably influenced by 
capillary activity. 

The tendency of diffusion is to equalize the concentration 
of a solution as to the ions and molecules of its solute, the 
molecules and ions of different salts moving more or less inde- 

loss of water. It is a shrinkage of the protoplasm and when carried 
beyond a certain point permanently injures the cell. 

^ Bouyoucos, G. J., The Freezing Point Method as a New Means of 
Measuring the Concentration of the Soil Solution Directly in the Soil ; 
Mich. Agr. Exp. Sta., Tech. Bui. 24, 1915. 



292 



NATURE AND PROPERTIES OF SOILS 



pendently. The absorption of nutrients by plants, in its 
simplest analysis, is but a working out of this phenomenon. 
Thus, if the concentrations of K+ ions is high in the soil 
solution and low within the cell, the potassium will move 
inward in response to diffusion forces, providing, of course, 
the ions can pass through the cell wall. This penetration is 
entirely independent of the entrance of water, as far as the 





Fig. 51. — Left, wheat seedling with 
soil particles clinging to root-hairs. 
Above, root-hairs much enlarged. 
Eoot-hairs are simple tube-like pro- 
longations of the border cells. 



movement of the latter is concerned. Moreover, the equaliza- 
tion of one ion is more or less unrelated to the concentration 
equilibrium of any other. The osmosis of the water, on the 
other hand, is a phenomenon dependent on sum-total concen- 
tration plus the semi-permeable membrane. 

154. Differential diffusion. — The intake of nutrients is 
by no means as simple as the above explanation might lead one 
to assume, due to the complications interposed by the presence 
of a semi-permeable membrane. The passage of ions and mole- 
cules through the cell-wall and the protoplasmic membrane 



REMOVAL OF NUTRIENTS FROM THE SOIL 293 

may be a simple mechanical infiltration, although it is prob- 
ably accompanied by a chemical reaction, or by a change in 
the colloidal state of the membrane or both. Moreover, differ- 
ent ions and molecules do not pass through the same cell-wall ^ 
with equal facility. Thus, one kind of ions may pass through 
very readily while another kind may encounter extreme diffi- 
culty in responding to diffusion tendencies. 

Differential diffusion may be ascribed to two conditions: 
(1) different relationships between the cell-wall and the ions 
and molecules of the entering material; and (2) differences 
in the rate at which the entering molecules and ions are 
utilized in the metabolic activities of the cell in particular and 
the plant as a whole. The first case has been partially ex- 
plained. If a compound ionizes into A and B ions and if A 
ions, due to their relationship to the colloidal cell-wall, enter 
more easily, a residue of B ions will be left in the soil solution. 

The second ease may be illustrated by assuming the pres- 
ence of potassium chloride in the soil solution. It ionizes 
K"" and 01" ions. Now conceive that these ions diffuse through 
the cell-wall with equal facility in response to equilibrium 
tendencies. If the potassium ions are used by the cell as 
rapidly as they enter and are removed from solution, more 
potassium will be absorbed. This might continue until the 
potassium ions in the soil solution become much reduced in 
number. If the chlorine, on the other hand, is but slightly 
utilized by the plant, little will be drawn from the soil after 
the initial equalization. Thus, a residue of chlorine might be 
left from this type of differential absorption. This applica- 
tion of diffusion principles shows the possibility, or even more, 
the probability of plants leaving residues in the soil solution. 
What the residues from different fertilizers may be and what 
is the practical importance of such differential actions are 
pertinent questions. 

' The term cell-wall as used here refers to the cell-wall proper plus 
the protoplasmic membrane. 



294 NATURE AND PROPERTIES OF SOILS 

155. Fertilizer residues may be developed in two gen- 
eral ways: (1) by selective absorption by the soil; and (2) by 
differential diffusion into the plant. Regarding the first case 
(see par. 141), it has already been established that soils 
ordinarily absorb the basic ions more strongly than the acid 
radicals, thus tending to leave an acid residue in the soil solu- 
tion. Sodium nitrate, ammonium sulfate, calcium nitrate, 
potassium chloride and potassium sulfate, therefore, tend to 
produce an acid residue, when they are first added to a soil. 

The final result, however, cannot be determined until the 
action of the crop is known. If the crop especially utilizes 
the cation or basic radical, it will intensify the selective ab- 
sorption of the soil and a still more pronounced acid residue 
will result. This would be the case with ammonium sulfate, 
potassium sulfate, and potassium chloride. If, however, the 
anion or acid radical is utilized to the greater extent, the ac- 
tion of the soil absorption would be nullified and an alkaline 
residue would tend to develop. This is especially true with 
sodium nitrate when applied in large amounts over a term of 
years, the physical condition of the soil becoming impaired 
due to the presence of sodium carbonate.^ 

One other condition is possible. If the plants should use 
the cation and anion of a fertilizer salt in equal proportions, 
no residue would result. This seems to happen to an approxi- 
mate degree with ammonium nitrate, potassium phosphate, 
potassium nitrate, and ammonium phosphate. Such salts are 
extremely valuable in long-continued experiments, where the 
disturbing effects of fertilizer residues are to be avoided. 
Monocalcium phosphate, the important constituent of acid 
phosphate, needs especial consideration. When added to the 
soil, it immediately reverts to the tricalcium form if active 
calcium is present.- Even with the large amount of gypsum 

* Hall, A. D., The Effect of the Long Continued Use of Sodium Nitrate 
on the Constitution of the Soil; Trans. Chem. Soc. (London), Vol. 85, 
pp. 950-971, 1904. 

='CaH,(PO,), -f 2CaH2(C03)2 = Ca3(P04)2 -f 4H,0 + 400^ 



REMOVAL OF NUTRIENTS FROM THE SOIL 295 

carried by acid phosphate, the effect does not seem to be 
towards acidity even after long periods of application.^ 

This discussion, brief as it is, brings out a little studied 
phase of crop and fertilizer interaction. How the plant util- 
izes a particular fertilizer after it is once in the soil, what 
residues are left, and the importance of such residues, are 
questions of fundamental concern. The possibility of plants 
influencing the soil and the fertilizers added, as well as the 
soil and fertilizer influencing the crop, is well worth attention, 

156. Do plants directly aid in the preparation of their 
nutrients? — The conception commonly held regarding the 
plant is that its direct relation to the soil is more or less 
passive. Indirectly, of course, it may exert a considerable 
influence on the availability of the nutrients. In view of the 
knowledge regarding fertilizer residues and the new concepts 
as to possible root exudates, the idea that the plant may 
directly aid in the preparation of its own nutrients is becom- 
ing more and more plausible. 

Such influences, if recognized, might occur in three ways: 
(1) through the action of carbon dioxide, known to be given 
off in large amounts by roots; (2) through the influence of 
organic and inorganic acids other than carbonic acid; and 
(3) by catalytic agents, enzymic or non-enzymic. 

In a rich, moist soil the number of root-hairs is very large 
and the relationship between the rootlets and the soil particles 
very intimate. When in contact with a particle of soil or 
colloidal complex^ the root-hair in many cases almost incloses 
it, and by means of its mucilaginous wall forms a contact so 
close as to make the solution held between the particle and the 
cell-wall distinct from that in the soil proper. Carbon dioxide, 
excreted under such conditions, may assume a solvent power 
entirely unique and independent of the amount produced. 

* Conner, S. D., Acid Soils and the Effect of Acid Phosphate and 
Other Fertilisers Upon Them; Jour. Ind. and Eng. Chem., Vol. 8, No, 1, 
pp. 35-40, Jan. 1916. 



296 NATURE AND PROPERTIES OF SOILS 

The plant might thus facilitate special conditions and aid ma- 
terially in the preparation of its own nutrients. 

Sachs/ and later other investigators, grew plants of various 
kinds in soil and other media in which was placed a slab of 
polished ' marble or dolomite or calcium phosphate, covered 
with a layer of washed sand. After the plants had made 
sufficient growth the slabs were removed, and on the surfaces 
were found corroded tracings, corresponding to the lines of 
contact between the rootlets and the minerals. 

Czapek ^ repeated the experiments of Sachs, using plates 
of gypsum mixed with the ground mineral that he wished 
to test, and this mixture he spread over a glass plate. Cza- 
pek found that, while plates of calcium carbonate and of 
calcium phosphate were corroded by the roots, plates of alu- 
minum phosphate were not. He concludes that if the tracings 
are due to acids excreted by the roots, these acids must 
be those that have no solvent action on aluminum phos- 
phate. This would limit the excreted acids to carbonic, 
acetic, proprionic, and butyric. By means of micro-chem- 
ical analyses of the exudations of root-hairs grown in a 
water-saturated atmosphere, Czapek found potassium, mag- 
nesium, calcium, phosphorus, and chlorine in the exudate. He 
concludes that the solvent action of roots is due to acid salts 
of mineral acids, particularly acid potassium phosphate. He 
has not proved, however, that the exudations were not from 
dead root-hairs or from the dead cells of the root cap. In 
either case they would have some solvent action, but whether 
sufficient to make them of importance is doubtful. This ob- 
jection makes the possible exudation of organic and inorganic 
acids somewhat questionable. 

Molisch^ found that root-hairs secrete a substance having 

^ Sachs, J., Auflosung des Marmors durch Mais-Wurslen ; Bot. Zeitung, 
18 Jahrgang, Seite 117-119, 1860. 

= Czapek, J., Zur Lehre von den Wurselausscheidung ; Jahrb. f. Wiss. 
Bot., Band 29, Seite 321-390, 1896. 

^Molisch, H., vber Wtirselausscheidungen und deren Eimrirlung auf 



REMOVAL OF NUTRIENTS FROM THE SOIL 297 

properties corresponding to those of an oxidizing enzyme. 
His work has been repeated by others, who have failed to ob- 
tain similar results, but lately Schreiner and Reed ^ have 
demonstrated an oxidizing action of roots that is apparently 
due to a peroxidase. Oxidation alone, however, would hardly 
suffice to account for the solvent action accompanying the de- 
velopment of roots, although it is doubtless an important 
function and useful in other ways. 

Schreiner and Sullivan - have demonstrated the presence 
of reducing substances in media in which plants were grow- 
ing. This work has recently been corroborated by Lyon and 
Wilson,^ working with maize, oats, peas, and vetch. They 
found that the solutions in which the plants had been growing 
exhibited both reducing and oxidizing phenomena. Reducing 
substances were always present, but whether oxidizing mate- 
rials were so consistently produced could not be definitely 
decided. The peroxidases were rendered inactive by boiling 
the solutions. The reducing substances did not always disap- 
pear with such treatment. This would throw some doubt upon 
the enzymic character of the reducing materials and suggest 
that non-enzymic catalytic exudates are a possibility. 

The interstices between the larger particles of a norma] 
soil are at least partially filled v/ith colloidal material of a 
more or less gel-like nature. Moreover, the surfaces of some 
soil grains may be somewhat coated with the same material. 
Roots of growing plants have been found to cause coagula- 
tion of at least some colloids, possibly by leaving an acid 
residue in the nutrient solution by reason of the selective 

Organische Substansen; Sitzungsber. Akad. Wiss. Wien-Math. Nat., Band 
96, Seite 84-109, 1888. Abstract in Chem. Centrlb. f. Agr. Chem., Band 
17, Seite 428, 1888, 

'Schreiner, Oswald, and Reed, H. S., Studies on the Oxidising Powers 
of Roots; Bot. Gazette, Vol. 47, p. 355, 1909. 

''Schreiner, 0., and Sullivan, M. K., Studies in Soil Oxidation; U. S. 
Dept. Agr., Bur. Soils, Bui. 73, 1910. 

'Lyon, T. L., and Wilson, J. K., Liberation of Organic Matter by 
Soots of Growing Plants; Cornell Agr. Exp. Sta., Memoir 40, July, 1921. 



298 NATURE AND PROPERTIES OF SOILS 

absorption of bases and rejection of the acid radicals of the 
dissolved salts. It is conceivable that the root-hairs, by re- 
moving bases from the solution existing between the cell-wall 
and the colloidal covering of the soil particle, may cause 
coagulation of the colloidal matter and thus liberate the nu- 
trient materials held by absorption. The liberated material, 
being of a readily soluble nature, would be taken up by the 
solution between the rootlet and the soil particle, from which 
the root-hair could readily absorb it. Such an hypothesis 
would account for the ability of plants to obtain a quantity 
of nutrients far in excess of that accounted for by the solvent 
action of pure water, and even beyond what many investi- 
gators are willing to attribute to the solvent action of water 
charged with carbon dioxide. 

157. The present status of the question. — The available 
evidence on excretion of acids other than carbonic by the 
roots of plants does not admit of any very satisfactory conclu- 
sion as to their relative importance in the acquisition of plant 
nutrients. There can be no doubt, however, that carbon 
dioxide resulting from root exudation and from decomposi- 
tion of organic matter in the soil plays a very prominent part 
in this operation. The very large quantity of carbon dioxide 
in the soil, amounting in some cases to nearly 10 per cent, of 
the soil air, or several hundred times that of the atmospheric 
air, must aid greatly in dissolving the soil particles. 

Whatever may be the concentration of the soil-water, it 
seems probable that the liquid that is found where the root- 
hair comes in contact with the soil particle, and that is sepa- 
rated, in part at least, from the remainder of the soil-water, 
must have a composition different from that found elsewhere 
in the soil. Many plants grown in solutions of nutritive salts 
have few or no root-hairs, but absorb through the epidermal 
tissue of the roots. The special modification by which the 
root-hairs come in intimate contact with the soil particle and 
almost surround it, indcates a direct relation between the 



REMOVAL OF NUTRIENTS FROM THE SOIL 299 

soil particles and the plant, as well as between the soil-water 
and the plant. Such a condition complicates in no small 
degree the practical questions of soil management and plant 
nutrition. 

158. Why crops vary in their ability to thrive on dif- 
ferent soils. — It is very commonly recognized that crops of 
different kinds vary in their ability to obtain nourishment 
from the soil. The difference between the nitrogen, phosphoric 
acid, potash, and lime taken up by an average corn crop and 
a wheat crop of average size is striking. The terms "weak 
feeders" and ** strong feeders," so often heard, indicate the 
practical field relationships. Aside from the fact that crops 
do not all need the same quantities of nutrients these differ- 
ences in ability to grow normally on different soils may be 
due either to (1) a larger absorbing system or (2) a more 
active absorptive capacit3^ 

Plants with large root systems may be expected to absorb 
greater amounts, not only of water but of nutrients also.^ 
Such a development is especially important in time of drought 
and in addition gives the plant a greater area from which to 
draw nutrients. Water, as well as nutrients, does not move 
through any great distance towards the imbibing and ab- 
sorbing surfaces. Root development, while of some impor- 
tance in explaining the differences in the feeding capacities 
of plants, is probably by no means as important as differences 
in the absorption activity. 

The absorptive activity of a plant under any given condi- 
tion of soil, climate, and stage of growth depends on: (1) the 
concentration and composition of the cell-sap; (2) the char- 
acter of the cell- wall; (3) the activity of the cell in elabo- 
rating and removing from solution the materials absorbed; 
(4) the extent to which exudates — whether these be carbon 

^ Gile, P. L., and Carrero, P. L., Absorption of Nutrients as Affected 
by the Number of Boots Supplied with the Nutrient; Jour. Agr. Ees., 
Vol. IX, No. 3, pp. 73-95, 1917. 



300 NATURE AND PROPERTIES OF SOILS 

dioxide, organic or mineral acids and their salts or enzymes 
— act on the colloidal and non-colloidal soil constituents; and 
(5) synergistic relationships in the soil solution or the cell- 
wall. 

The concentration and composition of the cell-sap deter- 
mines not only the osmotic relationship but has much to do 
with diffusion tendencies. The ability of the plant to obtain 
water and nutrients is thus directly affected by such condi- 
tions. The character of the cell-wall has of course an im- 
portant influence on such phenomena. If the cell-wall is 
easily penetrated, it may greatly facilitate the absorbing ca- 
pacity of the plant. If it is slowly penetrated or exerts spe- 
cial differential influences, it might have a great deal to do 
with the differences observed between certain plants. The 
character of the cell-wall has already been shown to be in- 
volved in the development of certain residues in the soil. 

The rate at which materials are utilized within the plant 
is also a factor. If ions or molecules are used rapidly and 
thus removed from solution, the diffusion of similar ions and 
molecules is hastened. Such activity would also influence 
osmotic relationships to a marked extent. This has already 
been discussed under differential diffusion. 

It is readily conceivable that exudates, insofar as they are 
capable of directly affecting the solubility of nutrients, might 
produce marked differences between plants as far as their 
absorbing activities are concerned. A crop producing active 
exudates of any kind should be able, other conditions being 
equal, to grow to better advantage, especially on a soil in 
which the necessary nutrients are somewhat unavailable. 

The absorption of electrolytes by plants seems to be influ- 
enced by the presence of other nutrient ions. True ^ has 
shown that K+ ions when accompanied by Ca^+ ions are readily 
absorbed by the seedlings of certain plants. When the same 

* True, E. H., TJie Function of Calcium in the Nutrition of Seedlings; 
Jour. Amer. Soc. Agron., Vol, 13, No. 3, pp. 91-107, 1921. 



KEMOVAL OF NUTRIENTS FROM THE SOIL 301 

concentration of potassium is offered in single solution, this 
nutrient is more or less neglected by the seedlings. This rela- 
tionship, by which the calcium ions make the potassium physi- 
ologically available, is spoken of by True as synergism ^ and 
probably has a great deal to do with the penetration of nu- 
trient ions into the plant. It is no doubt of considerable im- 
portance in acid soils where the active calcium is low. 

159. The absorptive capacity of different crops. — 
Cereals have the power of utilizing the potassium and phos- 
phorus of the soil to a considerable degree, but they generally 
require fertilization with nitrogen salts. Most of the cereals, 
such as wheat, rye, oats, and barley, take up the principal 
part of their nitrogen early in the season, before the nitrifica- 
tion processes are sufficiently operative to furnish a large 
supply of nitrogen ; hence nitrogen is the fertilizer constituent 
that usually gives good results, and should be added in a 
soluble form. Wheat, in particular, needs a large amount of 
available nitrogen early in its spring growth. Since it is a 
"delicate feeder," it does best after a cultivated crop or a 
fallow, by which the nitrogen has been converted into a soluble 
form. Oats can make better use of the soil nutrients and do 
not require so much manuring. Maize is a very ''coarse 
feeder," and, while it removes a large quantity of plant nu- 
trients from the soil, it does not require that this shall be 
added in a soluble form. Farm and other slowly acting ma- 
nures may well be applied for the maize crop. The long 
growing period required by maize gives it opportunity to 
utilize the nitrogen as it becomes available during the summer, 
when ammonification and nitrification are active. Phosphorus 
is the substance usually most needed by maize. 

Grasses, when in meadow or in pasture, are greatly bene- 
fited by manures. They are less vigorous ''feeders" than the 
cereals, have shorter roots, and, when allowed to grow for 
more than one year, the lack of aeration in the soil causes the 

* The term is used here in the sense of cooperation. 



302 NATURE AND PROPERTIES OF SOILS 

decomposition of soil organic matter to decrease. There is 
usually a more active fixation of nitrogen in grass lands than 
in cultivated lands, but this nitrogen becomes available very 
slowly. 

Different soils and climatic conditions necessitate varied 
methods of manuring for grass. Farm manures may well be 
applied to meadows in all situations, while the use of available 
nitrogen in commercial fertilizers is generally profitable. 

Most of the leguminous crops are deep-rooted and are vigo- 
rous "feeders." Their ability to take nitrogen from the air 
makes the use of that fertilizer constituent unnecessary ex- 
cept in a few instances, such as young alfalfa on poor soil, 
where a small application of nitrate of soda is usually bene- 
ficial. Phosphoric acid and often lime are the substances most 
beneficial to legumes on most soils. 

Many crops will utilize very large quantities of nutrients 
if they are in a form in which they can be used. Phosphates 
and nitrogen are the substances generally required, the latter 
especially by beets and carrots. In growing vegetables the 
object is to produce a rapid growth of leaves and stalks rather 
than seeds, and often this growth is made very early in the 
season. As a consequence a soluble form of nitrogen is very 
desirable. Farm manure should also have a prominent part 
in the treatment, as it keeps the soil in a mechanical condition 
favorable to the retention of moisture, which vegetables re- 
quire in large amounts, and it also supplies needed fertility. 
The very intensive method of culture employed in the produc- 
tion of vegetables necessitates the use of much greater quan- 
tities of manures than are used for field crops, and the great 
value of the product justifies the practice. 

160, Quantities of nutrients removed by crops. — The 
utilization of nutrient substances by crops is a constant source 
of loss of fertility to agricultural soils. In a state of nature 
the loss in this way is comparatively small, as the native vege- 
tation falls on the ground, and in the process of decomposi- 



REMOVAL OF NUTRIENTS FROM THE SOHj 303 

tion the ash is almost entirely returned, while there is a large 
gain of organic matter and often an increase in nitrogen as 
well. Under natural conditions the soil usually increases in 
fertility; for, while there is some loss through drainage and 
other sources, this is more than counterbalanced b}^ the action 
of the natural agencies of disintegration and decomposition, 
while the fixation of atmospheric nitrogen affords a constant, 
though small, supply of that important soil ingredient. 

When land is placed under cultivation a very different 
condition is presented. Crops are removed and only par- 
tially returned at best to the soil as manure and crop resi- 
due. A certain proportion of the soil nutrients are, therefore, 
permanently withdrawn. The point of vital importance, 
however, is that only a part of the total supply of soil con- 
stituents will ever become available, the portion withdrawn 
each year by cropping being a more serious consideration 
than is generally supposed. 

The following table, computed by Warington,^ shows the 
quantities of nitrogen, potash, phosphoric acid, lime and sulfur 
trioxide - removed from an acre of soil by some of the common 
crops. The entire harvested crop is included. 

Table LXVI 



Crop 


Yield 


Ash 

(LBS.) 


N 

(LBS.) 


K,0 

(lbs.) 


CaO 

(lbs.) 


P2O, 

(lbs.) 


SO3 

(lbs.) 


Wheat 

Barley 

Oats 

Maize 

Meadow Hay 
Red Clover . . 
Potatoes. . . . 


30 bushels 
40 bushels 
45 bushels 
30 bushels 
11/^ tons 
2 tons 
6 tons 


172 
157 
191 
121 

203 
258 
127 


48 
48 
55 
43 
49 
102 
47 


28.8 
35.7 
46.1 
36.3 
50.9 
83.4 
76.5 


9.2 

9.2 

11.6 

32.1 

90.1 

3.4 


21.1 

20.7 
19.4 
18.0 
12.3 
24.9 
21.5 


15.7 
14.3 
19.7 
12.0 
11.3 
15.4 
11.5 



^Warington, R., Chemistry of the Farm; pp. 64-65, London, 1894. 

'From Hart, E. B., and Peterson, W. H., Sulphur Requirements of 
Farm Crops in Relation to the Soil and Air Supply ; Wis. Agr. Exp. Sta., 
Res. Bui. 14, 1911. 



304 NATURE AND PROPERTIES OF SOILS 

Before the question of possible soil exhaustion can be dis- 
cussed adequately, the losses of nutrients in the drainage 
water must be considered as another source of loss in addition 
to the cropping influences already noticed. 

161. Qualitative composition of drainage water. — In 
theory, at least, the qualitative composition of drainage water 
should be the same as that of the soil solution; that is, in it 
should be found all of the common bases and acid radicals. 
Actually, however, due to the absorptive power of the soil, 
certain constituents appear in very slight amounts. Phos- 
phorus, for example, often occurs in drainage only in traces, 
as do the nitrites, ammonia, and carbonates. The principal 
bases lost by leaching are calcium, magnesium, potassium, 
and sodium. The important acid radicals of drainage water 
are the nitrates, chlorides, sulfates, and bicarbonates. 

As might be expected, the constituents appearing in drain- 
age are extremely variable not only when different soils are 
compared but also within the same soil at different periods. 
Phosphorus may be leached from some soils in measureable 
quantities, while from others the amount may be negligible. 
Nitrate nitrogen is usually an important constituent in all 
drainage water during the summer, especially that from a bare 
soil. In the winter and early spring nitrates decrease in 
amount. The method of soil treatment as to cultivation, ma- 
nuring, liming, or fertilizing may also markedly influence the 
qualitative composition of the water draining from field soil. 

162. Quantitative composition of drainage water. — While 
but little reliable data regarding the composition and 
especially the concentration of the soil solution are available 
at the present time, much exact information has been obtained 
regarding drainage water. The concentration of drainage 
water is much lower than that of the soil solution and much 
less variable. The total concentration seems to be governed 
more by the amount of water leaching through than by any 
other factor. Other seasonal conditions of course come into 



REMOVAL OF NUTRIENTS FROM THE SOIL 305 

play. In total concentration, drainage water seldom exceeds 
500 parts per million. It is thus much more dilute than the 
average soil solution. This difference holds for the separate 
constituents as well as for the concentration in toto. 

The following data, as compiled by Hall,^ give some idea 
of the quantitative composition of the drainage water from 
the clay loam soil of the Rothamsted Experimental Farm, 
The drainage water was obtained from tile drains, a line of 
which extended under each of the variously treated plats. 
The data is a mean of five collections, 1866 to 1868, 

Table LXVII 



Treatment 






Parts per 


Million Based on Solution 






N2O5 


NH3 


P2O5 


K2O 


CaO 


MgO 


NazO 


FeoOs 


CI 


SO3 


SiOa 


No manure 

Farm manure, 14 


3.9 

16.1 
5.1 

16.9 

18.4 


.12 

.16 
.13 

.27 

.24 


.63 

.91 

.17 


1.7 

5.4 
5.4 

2.7 

4.1 


98.1 

147.4 
124.3 

197.3 

118.1 


5.1 

4.9 
6.4 

8.9 

5.9 


6.0 

13.7 
11.7 

10.6 

56.1 


5.7 

2.6 
4.4 

2.7 

5.1 


10.7 

20.7 
11.1 

39.4 

12.0 


24.7 

106.1 
66.3 

89.7 

41.0 


10.9 
35.7 


Minerals - only. . 
Minerals plus 600 

lbs. (NH4)2S04 
Minerals plus 550 

lbs. NaNOa..., 


15.4 
20.9 
10.6 



It is immediately noticeable that ammoniacal nitrogen and 
phosphoric acid are lost in drainage to but a slight degree. 
Calcium appears in the highest concentration with sulfur 
next. Nitrates and potash are present in appreciable quan- 
tities but are quite variable. 

The influence of treatment is particularly obvious on the 
parts per million of nitrate nitrogen, lime, and sulfur appear- 
ing in the drainage, the addition of farm manure increasing 
all of these constituents as well as the concentration of the 
potash, soda, and chlorine. The application of sodium nitrate 
increased the nitrate nitrogen as well as the soda, potash, and 

^ Hall, A. D., The Bool- of the Bothamsted Experiments; pp. 237-239, 
New York, 1917. 

^ By minerals are meant the phosphoric acid, potash, lime, and other 
constituents left as ash when plants are burned. 



306 NATURE AND PROPERTIES OF SOILS 

lime. The two latter constituents are probably liberated by 
basic exchange. The addition of any fertilizer seems espe- 
cially to increase the lime in the drainage water. This is prob- 
ably due to the development of acid fertilizer residues. In 
general, it seems that the more productive the soil and the 
heavier the fertilization, the higher the concentration of the 
constituents in the drainage water. 

It is not always the case, however, that a manured soil 
loses more nutrient material than an unfertilized one. Ger- 
lach ^ reports experiments with soil tanks at the Bromberg 
Institute of Agriculture, in which five soils rationally fertil- 
ized yielded larger crops and lost in the main less nitrogen 
and lime in the drainage water than the same soils unmanured. 
The loss of potash was slightly greater from the manured than 
from the unmanured soils. Apparently the stimulation that 
the plants received from the fertilizer enabled them to make 
such a good growth that they absorbed more soluble nitrogen 
and lime in excess of the unfertilized plants than was added 
in the fertilizer, and nearly as much potash. 

The most serious losses of plant nutrients in drainage are 
those of the nitrogen and calcium, both of which losses are to 
a certain extent unavoidable. These losses are also very 
closely related, rising and falling together. Nitrogen is lost 
as the nitrate while the calcium is leached out due to the 
presence of the bicarbonate and nitrate radicals. While loss 
of lime goes on continually, it is of necessity particularly 
large during periods of rapid nitrate accumulation. Nitrogen 
is a high-priced fertilizer constituent, while a continued loss 
of lime tends to produce soil acidity. About the only means 
of conserving either of these constituents is to maintain a crop 
on the soil, especially during the warmer seasons. 

^ Gerlach, M., uber die durch Siclcerwasser dem Boden Entsogenen 
Menge Wasser und Nahrstoffe ; Illus. Landw. Zeitung, 30 Jahrgang, 
Heft 95, Seite 871-881, 1910. Also, Untersuchungen iiber die Menge und 
Zusammensetsung der Siclcerwasser ; Mitt. K. W. Inst. f. Landw. in 
Bromberg, Band 3, Seite 351-381, 1910. 



REMOVAL OF NUTRIENTS FROM THE SOIL 307 

163. Quantities of nutrients removed by drainage and 
cropping. — Now that an adequate coueeption has-])een pre- 
sented regarding the composition of soil drainage water and 
also of the nutrients removed by cropping, it is interesting to 
note what the combined result may be on the same soil. Such 
information can be obtained only in a few instances. The 
following data from the lysi meters at the Cornell Experiment 
Station ^ are valuable in this respect.- The soil used was a 
Dunkirk silty clay loam. 

Table LXVIII 

average annual, loss of nutrients by percolation and 

cropping. cornell lysimeter tanks. 

average op 10 years. 







Pounds 


TO THE Acre per Year 


















N 


P2O5 


K,0 


CaO 


SO3 


Drainage losses 












Bare 


69.0 


— 


86.4 


557.0 


132.0 


Rotation .... 


7.3 


— 


68.7 


345.9 


108.5 


Grass 


2.5 


— 


74.0 


363.8 


111.0 


Crop removal 












Bare 


— 


— 


— 


— 


— 


Rotation .... 


70.5 


43.5 


105.4 


24.3 


41.0 


Grass 


54.4 


28.6 


74.0 


12.8 


29.2 


Total loss 












Bare 


69.0 


— 


86.4 


557.0 


132.0 


Rotation .... 


77.8 


43.5 


174.1 


370.2 


149.5 


Grass 


56.9 


28.6 


158.0 


376.6 


140.2 



* Unpublished data, Cornell Agr. Exp. Sta., Ithaca, N. Y. 

° A study was made at the New Jersey Experiment Station of the 
nitrogen losses from a loam soil in cylinders under a five-year rotation 
of corn, oats, wheat and timothy for 20 years, treated in various ways 
as to lime, manure and fertilizers. The average loss of nitrogen from 
the surface ten inches of soil for 1.5 years was 103 pounds annually 
due to cropping and leaching. Data were obtained by analyzing the 
soil and the crops. Lipman, J. G., and Blair, A. W., Nitrogen Under 
Intensive Cropping ; Soil Sci., Vol. XII, No. 1, pp. 1-16, July, 1921. 



308 



NATURE AND PROPERTIES OF SOILS 



The first outstanding feature of the above table is the con- 
trol on drainage losses exerted by cropping. The loss of 
nitrate nitrogen is reduced to an exceptionally low figure, 
while the saving of potash, sulfur, and lime is quite apprecia- 
ble. No phosphoric acid is lost even from the bare soil. The 
losses due to cropping and leaching combined from a planted 
soil are generally but little greater than the drainage losses 
alone from a soil kept continuously bare except in the cases 
of the phosphoric acid and the potash. 

The next point of interest is the difference in the nutrients 
removed by a rotation of crops, such as maize, oats, wheat, 
and hay as compared with permanent meadow. The latter, 
although absorbing less nutrients than the rotation crops, 
exert as marked a conserving effect on the nutrients appear- 
ing in the drainage as do the crops in rotation. The compara- 
tive removal of nutrients from the soil by cropping and leach- 
ing are well shown by the following diagram, in which the 
weight of the symbols indicates where the loss of any par- 
ticular nutrient is the greater. 



RELATIVE LOSSES OF NUTRIENTS FROM A PLANTED SOIL THROUGH 
CROPPING AND DRAINAGE 





Nitrogen 


Phos- 
phoric 

ACID 


Potash 


Lime 


Sulfur 
Trioxide 


Cropping loss 

Drainage loss. . . . 


N 

N 


P.O. 

P.O. 


K,0 
K'O 


CaO 
CaO 


SO3 
SO3 



164. Possible exhaustion of the soil. — It is interesting at 
this point to compare the amounts of nutrients removed an- 
nually from a soil cropped in rotation with the amounts which 
are present in an average soil to the depth of four feet. As- 
suming reasonable figures for the pounds of sulfur trioxide, 
lime, phosphoric acid, nitrogen, and potash and considering 
that these nutrients are wholly available, the following sig- 



REMOVAL OF NUTRIENTS FROM THE SOIL 309 

nifieant data are obtained. The losses of nutrients by drain- 
age and rotation cropping are from the figures already quoted 
regarding the Cornell lysimeter soils. 

Table LXIX 

showing the number of years a soil to the depth op four 

feet would supply nutrients for crop growth, 

providing that all of these constituents 

were ttniformly available 



Constituents 


Pounds to 

THE Depth of 

FouE Feet 


Pounds 

Removed 

Annually by 

C'ropping and 

Drainage 


Years 


SO3 


12,000 
85,000 
16,000 
15,000 
250,000 


84.5 1 
370.2 
43.5 
46.8 1 
174.1 


142 


CaO 

P,0, 


229 
367 


N 


303 


K3O 


1,435 



While the subsoil supplies large amounts of plant nutrients, 
it must be remembered that only a small proportion of the 
soil constituents, especially the phosphoric acid and potash, 
ever become available either in surface or subsoil. Moreover, 
crop yields decrease as the nutrients, even those most readily 
available, are reduced. The above figures for duration of 
crop growth are, as a consequence, merely conventional but 
they indicate the probability of even a very fertile soil be- 
coming quickly exhausted. 

Moreover, when it is considered that the soil must be de- 
pended on to furnish food for humanity and domestic animals 
as long as they shall continue to inhabit the earth, the supply 
of plant nutrients becomes a matter of grave concern. 

The visible sources of supply, to replace or supplement 

* Sixty-five pounds of SO, are added an acre each year in rain- 
water while 31 pounds of N are added yearly to the acre in rain and 
through the free-fixing activity of organisms (pars. 222, 236 and 238). 



310 NATURE AND PROPERTIES OF SOILS 

those in the soils now cultivated, are, for the mineral sub- 
stances, the subsoil and the natural deposits of phosphates, 
potash salts, and limestone; and for nitrogen, deposits of 
nitrate, the by-products of coal distillation, and the nitrogen 
of the atmosphere. The last of these is inexhaustible, and the 
exhaustion of the nitrogen supply, which a few years ago was 
thought to be a matter of less than half a century, has now 
ceased to cause any apprehension. 

The conservation or extension of the supply of mineral 
nutrients is now of extreme importance. The utilization of 
city refuse and the discovery of new mineral deposits are 
developments well within the range of possibility, but neither 
of these promises to afford more than partial relief. The 
utilization of the subsoil through the gradual removal by nat- 
ural agencies of the topsoil will, without doubt, tend constantly 
to renew the supply. The removal of topsoil by wind and 
water erosion is, even on level land, a very considerable factor. 
The large amount of sediment carried in streams immediately 
after a rain, especiall}^ in summer, gives some idea of the ex- 
tent of this shifting. This affects chiefly the surface soil, and 
thereby brings the subsoil into the range of root action. 

There is little doubt that a moderate supply of plant nu- 
trients will always be available in most soils, but for progres- 
sive agriculture the use of green-manures, legumes and farm 
manures must be supplemented by judicious and economical 
application of lime and certain fertilizer constituents. 



CHAPTER XVI 
CHEMICAL ANALYSIS OF SOILS 

No PHASE of soil science has received as much popular rec- 
ognition as chemical analysis, nor is any other technical soil 
procedure so little understood in general and at the same 
time so greatly overrated. Many persons feel that a soil 
analysis should completely solve the many problems, both 
theoretical and practical, regarding the economic management 
of the soil, especially as to its fertilizer needs. In the light 
of such general misunderstanding in regard to the research 
and applied value of chemistry to soils, a consideration of the 
question seems opportune at this point, especially as the dis- 
cussion of the phenomena of absorption and the characteristics 
of the soil solution have just been presented. 

For convenience in treatment, chemical analyses, as applied 
to soils, may be grouped under two heads — total or bulk 
analyses and partial or extraction methods. In the former the 
total amount of certain constituents are determined regard- 
less of their chemical combinations and character. In the 
latter group of methods only a portion of certain important 
materials are removed and analyzed, the chemical combina- 
tion being to a certain extent a factor in the amount of any 
constituent extracted. 

165. Bulk analysis — organic carbon and nitrogen.^ — 

^ The sampling of the soil is an important consideration in any 
analytical work. The sample should be representative and is best 
taken with a soil auger. In sampling small areas, such as plats, a num- 
ber of boripgs are usually made to the depths required and thoroughly 
mixed. This composite is quartered until a sample of the required size 

311 



312 



NATURE AND PROPERTIES OF SOILS 



:a== 



The methods of determining the amount of organic matter in 
any soil have already been discussed (par. 60), the conclusion 
being that the figure for organic carbon, or this figure multi- 
plied by 1.724, was the most reliable indication of the organic 
content of a soil. The bomb method is cited as one of the 
more suitable procedures for obtaining 
the organic soil carbon. 

The method for estimating the soil 
humus, although it is not a bulk method, 
should be considered at this point because 
of its close relationship to the determina- 
tion of organic carbon. The modified 
Grandeau procedure (par. 61) is used for 
humus estimation and is supposed to dis- 
tinguish between the more active and less 
active organic matter. Of the two 
methods the determination of organic car- 
bon is by far the more accurate. As 
there is also some doubt about the com- 
parative activity of the material ex- 
tracted by the Grandeau procedure the 
figure for organic carbon seems in general 
the more significant and it is the deter- 
mination usually made. The estimation 
of soil humus may, therefore, be con- 
sidered as a chemical method of sec- 
ondary importance except in special 
cases. 
The total nitrogen of the soil is determined by either the 
Kjeldahl, the modified Kjeldahl, or by the Gunning method. 
The determination of nitrogen is such a common laboratory 



Pig. 52. — Auger used 
in the field exam- 
ination of soil and 
in taking samples. 
Note modified cut- 
ting edge. 



is obtained. Where large areas are involved, as in the case of a soil 
survey, only one sample, representative of the soil type being studied, is 
usually taken. 



CHEMICAL ANALYSIS OF SOILS 313 

procedure that it is worth while to consider the principles in- 
volved.^ About 10 grams of dry soil are placed in a Kjeldahl 
flask with about 30 c.c. of strong sulfuric acid and 0.7 gram 
of mercuric oxide or its equivalent in metallic mercury. The 
mixture is boiled vigorously until the solution is clear. The 
flask is then removed from the flame and, while hot, potassium 
permanganate is added in small quantities to complete the 
oxidation until, after shaking, the liquid remains a green or 
purple color. The nitrogen of the soil, no matter what has 
been its combination, is now in the form of ammonium sulfate 
[(NH4)2S04], the mercury acting as a catalytic agent and 
the permanganate as an oxidizer. 

After cooling, the contents of the flask are diluted with 
about 200 c.c. of water, zinc dust or a few pieces of granu- 
lated zinc are added to prevent bumping and 25 c.c. of 
potassium sulfid are poured in with shaking. Next a sodium 
hydroxide solution, suffcient in amount to neutralize the acid, 
is carefully poured dow^n the side of the flask. The flask is 
then connected with a condenser and the contents cautiously 
mixed by shaking. The ammonia set free by the alkali is dis- 
tilled over into a standard acid, the excess acid being titrated 
with a standard alkali, using a suitable indicator. When the 
amount of standard acid neutralized is known, the amount of 
nitrogen, which has passed over in the form of ammonia, may 
be calculated and expressed as a percentage, based on the 
original dry sample of soil. (See Fig. 53.) 

^ The method described above is the Kjeldahl method. See Official 
and Tentative Methods of Analysis of the Assoc. Official Agr. Chemists, 
p. 314, 1920. 

This method does not determine the nitrogen in the nitrate form. 
If this is desired a modified procedure must be followed. As the 
nitrate nitrogen in most soil is low compared to the nitrogen in other 
combinations, the objection just made to the regular Kjeldahl method 
is not serious. 

Snyder, E. S., Determination of Total Nitrogen in Soils Containing 
Bather Large Amounts of Nitrates; Soil Sci., Vol. VI, No. 6, pp. 487- 
490, 1918. 



314 



NATURE AND PROPERTIES OF SOILS 



166. Bulk analysis — complete solution of the soil. — By 

the use of hydrofluoric acid or by fusion witli potassium and 
sodium carbonate, the entire soil mass may be decomposed and 




Fig. 53. — Front and side view of a Kjeldahl distilling battery. (A), 
Kjeldahl flask; (B), trap; (C), condenser tank; (D), receiving flask 
containing standard acid and (E), Bunsen burner. 



its constituents determined.^ The amount of lime (CaO) or 
any other constituent,^ may thus be expressed in percentage 

^ Wiley, Harvey W., Principles and Practices of Agricultural Chemical 
Analysis, Vol. 1, pp. 398-399, 1906. 

* SchoUenberger presents some interesting data regarding the pro- 



CHEMICAL ANALYSIS OF SOILS 



315 



based on dry soil or in pounds to the acre to any suitable 
depth. This method gives only the total of any constituent 
and tells nothing regarding its availability to crops, although 
a marked deficiency in any element may thus be detected. A 
rock will often show greater amounts of the mineral elements 
than a fertile soil.^ 

167. Partial analysis of the soil for mineral constitu- 
ents. — AYhen it was realized that a bulk analysis of the soil, 
especially for the mineral constituents, gave no information 
as to the availability of certain elements or as to the fertilizer 
needs of the soil, extraction methods were devised. Such 
methods, of whatever character they may be, are designed to 

portion of organic and inorganic phosphorus in Ohio soils. The figures 
are an average of twelve types. 



Soils 


Total 
P.O. 


Organic P2O5 

AS Per Cent 

op Total 


Total 

N 


Cultivated 

0- 7 inches 

7-15 inches 

Virgin 

0- 7 inches 


% 

.0433 
.0345 

.0587 
.0381 


% 

34 

20 

24 
21 


% 

.14 
.07 

19 


7-15 inches 


08 







Schollenberger, C. J., Organic PJwspJwrus Content of Ohio Soils; 
Soil Sci., Vol. X. No. 2, pp. 127-141, 1920. 

For methods of determining organic phosphorus, see Potter, R. S., 
The Organic Phosphorus of Soil; Soil Sci., Vol. II, No. 4, pp. 291- 
298, 1916. 

Eost, C. O., The Determination of Soil Phosphorus; Soil Sci., Vol. 
IV, No. 4, pp. 295-311, 1917. 

Potter, R. S., and Snyder, R. S., The Organic Phosphorus of Soil; 
Soil Sci., Vol. VI, No. 5, pp. 321-332, 1918. 

Schollenberger, C. J., Organic Phosphorus of Soil: Experimental Work 
on Methods for Extraction and Determination ; Soil Sci., Vol. VI, No. 5, 
pp. 365-395, 1918. 

^ Sulfur is determined by a* separate method. Official and Tentative 
Metliods of Analysis of the Assoc, of Official Agr. Chemists, p. 317, 1920. 

See also, Hart, E. B., and Peterson, W. H., Sulphur Eequirements of 
Farm Crops in Eelation to the Soil and Air Supply; Wis. Agr. Exp. 
Sta., Res. Bui. 14, 1911. 



316 



NATURE AND PROPERTIES OF SOILS 



give information regarding the availability of the plant nutri- 
ents within the soil. They may be listed under three heads: 
(1) digestion with strong acids, (2) digestion with dilute 
acids, and (3) extraction with water. These methods will be 
discussed in the order mentioned. 

168. Digestion with strong acids. — While surfuric, ni- 
tric, and hydrochloric acids have all been used as solvents,^ 
the one most commonly employed is hydrochloric acid of 
1.115 specific gravity.^ It has been used to such an ex- 
tent that it may be considered the standard solvent, and a 
statement of a chemical analysis of a soil in this country may 
be considered as based on this solvent unless otherwise stated. 

An analysis by this method is supposed to show the propor- 
tion of nutrient materials in a soil that is in a condition to 
be used ultimately by plants at the time when the analysis is 
made. The nutrient materials that are not dissolved by 
treatment with hydrochloric acid are assumed to be in, a 
condition in whch plants cannot use them. The difficulty 
with this assumption is that, while treatment with hydro- 
chloric acid of a given strength marks a definite point in the 
solubility of the compounds in the soil, it does not bear a 
uniform relation to the natural processes by which these 
compounds become available to plants. 

This method is not only arbitrary but it is artificial as well. 



^ The following analyses of the same soil quoted from Snyder are 
interesting in this regard. Snyder, H., Soils; Minn. Agr. Exp. Sta., 
Bui. 41, p. 66, 1895. 



Extract 


Total 


K2O 


CaO 


MgO 


P2O5 


SO3 




% 


% 


% 


% 


% 


% 


HCl 


18.80 


.42 


.55 


.40 


.23 


.08 


HNO3 


16.55 


.30 


.30 


.32 


.23 


.08 


H2SO, 


19.55 


.52 


.53 


.52 


.26 


.10 







^ Official and Provisional MetJwds of Analysis; U. S. Dept. Agr., Bur. 
Cham., Bui. 107 (revised), pp. 14-18, 1908. 



CHEMICAL ANALYSIS OF SOILS 



317 



While it is supposed to measure the permanent fertility ^ of 
a soil, there is no reason to suppose that there is any rela- 
tionship between the nutrients extracted by a strong acid 
in the laboratory and the amounts of the same constituents 
absorbed by crops over a period of fifty or one hundred years. 
Moreover, productivity is not necessarily controlled by the 
amounts of available nutrients in a soil. This further vitiates 
the data obtained by such an analysis. 

Snyder ^ has analyzed a number of Minnesota soils by 
means of digestion with strong hydrochloric acid, decompos- 
ing the acid-insoluble residues by fusion and determining 
their composition. Veiteh ^ has analyzed certain Maryland 
soils by the hydrochloric acid method and by means of com- 
plete solution. A few examples are given below to show how 
soils may vary in the solubility of their constituents in strong 
hydrochloric acid: 

Table LXX 

percentage of soil constituents insoluble in 
HQ, SP. GR. 1.115 



Soils 

Minnesota (Snyder) 

Fair Haven 

Holden 

Experiment Station . 
Maryland (Veiteh) 

Columbia 

Chesapeake 

Hudson River Shale 



94 


CaO 


MgO 


P.O. 


25 


58 


40 


81 


61 


76 


45 


83 


41 


36 


18 


95 


90 


34 


66 


67 


82 


29 


15 


73 


37 


28 






SO, 



74 

90 
20 



169. Digestion with dilute acids. — A great number of 
different acids have been used in a dilute condition for ex- 

* Fertility is used here in the sense of potential productivity, the 
nutrients in the soil being considered as the controlling factor. 

^Snyder, Harry, Soils; Minn. Agr. Exp. Sta., Bui. 41, p. 35, 1895. 

'Veiteh, F. P., The Chemical Composition of Maryland Soils; Md. 
Agr. Exp. Sta., Bui. 70, p. 103, 1901. 



318 NATURE AND PROPERTIES OF SOILS 

tracting soils, the idea being in every case to determine the 
amount of the mineral nutrients immediately available to 
crops. The scope is thus narrower than in the digestion with 
strong acids, by which the permanent fertility is sought. 

Two acids have been commonly utilized in the extraction of 
soils with dilute solvents : one per cent, citric acid proposed by 
Dyer,^ and one-fifth normal nitric acid.^ Dyer adopted the 
one-per-cent. strength as the result of an investigation in which 
he determined the acidity of the juices in the roots of over 
one hundred species or varieties of plants representing twenty 
different natural orders. The implication is that plants pro- 
duce a solvent action on a soil in proportion to the acidity of 
their juices, but an examination of Dyer's figures does not 
show that the size of the crop ordinarily produced by the plants 
would in many cases correspond to the acidity of their juices. 
Thus, of the Cruciferae, the horse-radish has several times tlie 
acidity of the Swedish turnip or of the field cabbage, although 
the crop produced by the former is much less than that of the 
latter two. 

Dyer's method gave results on Rothamsted soils that en- 
abled him to estimate their relative productivity. On other 
soils and in the hands of other investigators, however, the 
method is unsatisfactory. In soils rich in calcium and low in 
iron and aluminum, it may often show the amounts of easily 
soluble phosphoric acid and potash. 

In ease of manipulation, the fifth normal nitric acid is 
preferable to the one-per-cent. citric acid, which is rather 
tedious to work with. It has been utilized nearly as exten- 
sively in this country as has the latter in Great Britain. Its 
use has been confined largely to the determination of the 
readily available phosphoric acid and potash in the soil, as 

* Dyer, Bernard, On the Analytical Determination of Probably Avail- 
able "Mineral" Plant Food in Soils; Jour. Chem. Soc, Vol. LXV, 
pp. 115-167, 1894. 

" Official and Provisional Methods of Analysis; U. S. Dept. Agr., Bur. 
Chem., Bui. 107 (revised), p. 18, 1908. 



CHEMICAL ANALYSIS OF SOILS 319 

has the citric acid method. It is obvious that some materials 
are more readily soluble than others, and for that reason the 
method will distinguish between phosphorus and potassium 
in different forms. The calcium phosphates are supposed to 
be entirely soluble in this strength of acid. According to 
Fraps/ it dissolves iron and aluminum phosphates to only a 
slight extent, thus distinguishing between these forms of phos- 
phorus and calcium phosphate. Fraps finds also that no 
potassium is removed from orthoclase and microcline, that less 
than 10 per cent, is dissolved from glauconite and biotite, and 
that from 15 to 60 per cent, is dissolved from muscovite, 
nephelite, leucite, apophyllite, and phillipsite, minerals known 
to be rather easily available. 

There are several factors, however, that make the use of 
one-fifth normal nitric acid an uncertain guide to the avail- 
able phosphoric acid and potash in the soil. When a soil is 
treated with the acid, some of it is neutralized by the reac- 
tions that result and thus its strength is lessened. This may 
have no relation to the quantities of phosphoric acid or potash 
dissolved. Some analysts correct for the neutralization and 
some do not. Again, as with concentrated hydrochloric acid, 
the degree of solubility of the soil constituents in the nitric 
acid may not correspond with the ability of the plant to ob- 
tain these substances. With this, as with the other methods 
discussed, the objection holds that the results cannot be taken 
as an infallible guide to the productiveness of a soil, or to its 
fertilizer needs. The artificial extraction of a soil in the 
laboratory cannot be expected to simulate the action of a 
crop even for one year. 

170. Extraction with water. — As carbon dioxide is a 
universal constituent of the water of the soil, and without 

^ Fraps, G. S., Active Phosphoric Acid and Its "Relation to the Needs 
of the Soil for Phosphoric Acid in Pot Experirfients ; Tex. Agr. Erp. 
Sta., Bui. 126, pp. 7-72, 1909. 

Also, The Active Potash of the Soil and Its Relation to Pot Experi- 
ments; Tex. Agr. Exp. Sta., Bui. 145, pp. 5-39, 1912. 



320 NATURE AND PROPERTIES OF SOILS 

doubt a potent factor in the decomposition of the mineral 
matter, it has been proposed to use a solution of carbon diox- 
ide as a solvent in soil analysis. The amounts of soil con- 
stituents taken up by this solvent are much less than are taken 
up by any of the others heretofore mentioned, but all mineral 
substances used by plants are soluble in it to some extent. 
The amount of phosphoric acid is so small as to make its 
detection by the gravimetric method difficult. Like other 
methods employing very weak solvents, this is open to the 
objection that much of the material dissolved cannot be re- 
moved because of the absorptive power of the soil, and as this 
varies with the character of the soil, adequate comparisons 
cannot be made. Water charged with carbon dioxide has been 
very largely replaced by pure water in making such extrac- 
tions. 

When soil is digested with distilled water, all the mineral 
substances used by plants are dissolved from it, but in very 
small quantities. It has been proposed to employ this extract 
for soil analysis on the ground that it is a natural solvent 
and dissolves only those nutrients in a condition to be used 
by plants. By determining the moisture content of the soil 
and using a known quantity of water for the extraction, the 
parts per million of the extracted nutrients may be expressed 
on the basis of the dry soil or of the solution. The aqueous 
extract does not by any means contain the entire quantity of 
nutrients which were in the soil solution and is not an exact 
measure of the fertility in this form. Absorption holds back 
an undetermined and variable quantity of the important con- 
stituents and thus vitiates the method, especally for compar- 
ing different soils. The method, however, is very valuable for 
comparing the same soil at different times, especially as re- 
gards the nitrates. The nitrate radical is not absorbed to any 
great degree by the soil and presents a very fair measure of 
the concentration of the soil solution as far as this constituent 
is concerned. 



CHEMICAL ANALYSIS OF SOILS 



321 



The water extract method generally followed in this country 
is that established by the Bureau of Soils. One hundred 
grams of soil are mixed with 500 cubic centimeters of water 
and stirred for three minutes. After standing twenty minutes 
the supernatant liquid is filtered through a Pasteur-Chamber- 
land filter under pressure. It is then ready for analysis. 
Colometric and turbidity methods are usually employed in de- 
termining the amounts of the constituents removed.^ The 
method is of greatest use in estimating the nitrate content of 
soils. 

The quantity of extracted material depends on the absorp- 
tive properties of the soil, on the amount of water used in the 
extraction, and on the number of extractions. Analyses of 
the aqueous extract of a clay and of a sandy soil from the 
Cornell University farm sejrve to illustrate the greater reten- 
tive power of the former for nitrates. Sodium nitrate was 
applied to a clay soil and to a sandy loam soil at the rate of 
640 pounds to the acre. Analyses of aqueous extracts some 
ninety days later showed the following : 

Table LXXI 



Kind of Soil 


Fertilizer 


Nitrates IN Soil 

(Parts per 

million) 


Clay 


Sodium nitrate 
No fertilizer 
Sodium nitrate 
No fertilizer 


7 8 


Clay 


1 8 


Sandy loam 

Sandy loam 


150.0 
29.7 



There was apparently a much greater retention of nitrate 
by the clay soil, as shown by a comparison of the fertilized 
and unfertilized plats on both soils. 

^ Schrciner, 0., and Failyer, G, H., Colorimetric, Turbidity and Titra- 
tion Methods Used in Soil Investigations; U. S. Dept. Aer., Bur. Soils, 
Bui. 31, 1906. 



322 



NATURE AND PROPERTIES OF SOILS 



Schulze ^ extracted a rich soil by slowly leaching one kilo 
with pure water, one liter of water passing through in twenty- 
four hours. The extract for each twenty-four hours was 
analyzed every day for a period of six days. The total amounts 
dissolved during each period were as follows : 



Table LXXII 



Successive Extraction 


Total Matter 
Dissolved 

GRAMS 


Volatile 

GRAMS 


Inorganic 

GRAMS 


First > 

Second 


.535 
.120 
.261 
.203 
.260 
.200 


.340 
.057 
.101 
.083 
.082 
.077 


.195 
.063 


Third 


.160 


Fourth 


.120 


Fifth 


.178 


Sixth 


.123 



It will be noticed that the dissolved matter, both organic 
and inorganic, fell off markedly after the first extraction. 
Later extractions were doubtless supplied largely from the 
substances held by absorption, which gradually diffused into 
the water extract as the tendency to maintain equilibrium of 
the solution overcame the absorptive action. "With the re- 
moval of the absorbed substances the equilibrium between 
the absorption and solution surfaces and the surrounding so- 
lution is disturbed, diffusion and solution are increased, and 
more material gradually passes from the soil into the solution. 
In this way, a more or less uniform and continuous extraction 
is mantained. 

In spite of the obvious defects of the water extraction 
method the work of Hoagland, Burd and Stewart - seems to 
indicate that such data, if obtained over an extended period, 



'Schulze, F., rber den Phosphorsaure-Gehalt des Wasser-Aussugs der 
Acker erde; Landw. Vers. Stat., Band 6, Seite 409-412, 1864. 

^ Burd, J. S.J Water Extractions of Soils as a Criteria of their Crop- 



CHEMICAL ANALYSIS OF SOILS 323 

are a good comparative measure of the concentration and 
composition of the soil solution (see par. 145). They also con- 
sider water extractions as criteria of the crop-producing power 
of a soil so studied. The practical value of such a method as 
a means of estimating fertility is, however, somewhat ques- 
tionable, since much time and labor are required to make the 
necessary extractions and analyses before conclusions at all 
reliable may be drawn. 

171. Fertility evaluation by means of chemical analyses. 
— The important part that chemistry plays in soil investiga- 
tion and research should not be overlooked. Nor can a satis- 
factory presentation of soil phenomena, whether with a tech- 
nical or an applied bearing, be made without the use of some 
chemistry. Chemistry, in fact, is the fundamental science 
that is most utilized in soil study. 

In spite of these relationships, the value of chemistry in the 
direct solution of practical fertility problems is neither abso- 
lute nor final. The objections already raised to the digestion 
of the soil, either with concentrated or dilute acids, shows the 
inadequacy of these methods so far as practical problems are 
concerned. 

Of all the chemical analyses discussed those that have to do 
with the determination of organic carbon, total nitrogen, total 
calcium and phosphoric acid are of outstanding value. Or- 
ganic matter is such an important soil constituent that a 
knowledge of its amount cannot fail to throw much light on 
the physical and chemical condition of the soil. Much of the 
soil nitrogen is carried by the organic matter and becomes 
available in much larger proportion than do the mineral 
nutrients. An analysis for total nitrogen is, therefore, a 

Producing Power; Jour. Agr. Res., Vol. XII, No. 6, pp. 297-309, 1918. 

Stewart, G. R., Effect of Season and Crop Groicth in Modifying the 
Soil Extract; Jour. Agr. Res., Vol. XII, No. 6, pp. 311-368, 1918. 

Hoagland, D. R., The Freezing Point Method as an Index of Varia- 
tions in the Soil Solution Due to Seaso7i and Crop; Jour. Agr. Res., 
Vol. XII, No. 6, pp. 369-395, 1918. 



324 NATURE AND PROPERTIES OF SOILS 

fairly reliable guide in some cases to the fertility of the soil 
under specific consideration. 

Although the relationship of organic matter and nitrogen 
to soil fertility is so close that certain generalized tables ^ may 
be cited for the interpretation of chemical data, no close cor- 
relation is possible, especially where soils of markedly different 
character are compared. So many other factors may enter 
that practically no opinion can be formed regarding the prod- 
uctivity of a soil unless other and more detailed data are 
available. 

An interesting example of where the nitrogen content fails 
to indicate the relative fertility of two soils is found in certain 
unpublished data from the Cornell Agricultural Experiment 
Station. Two soils are being studied in the lysimeter tanks — 
Dunkirk silty clay loam and Volusia silt loam. In Table 
LXXIII is given the nitrogen and calcium content of these 
soils and the pounds of nitrogen removed to the acre by maize, 
oats, and barley, respectively, for the years 1915, 1916, and 
1917. The treatment and handling of the soils compared has 
been the same. 

While the nitrogen, phosphoric acid and potash contents of 
these soils are about the same, a marked difference is noted in 
their productivity. This may be due, at least partially, to 
the calcium content, which is rather high in the Dunkirk, 
especially in the subsoil. In comparing soils over wide areas 

^ The following tentative classification of soils on the basis of their 
percentages of organic matter and nitrogen is offered for generalized 
field use: 



Description 



Percentage of 
Organic Matter 



Percentage of 
Nitrogen 



Low 

Medium . . . 
High .... 
Very high 



.0- 3.0 

3.0- 6.0 

6.0-10.0 

above 10.0 



.00- .10 

.10- .25 

.25- .40 

above .40 



CHEMICAL ANALYSIS OF SOILS 



325 



Table LXXIII 

the percentages of nitrogen and calcium in the dunkirk 

silty clay loam and the volusia silt loam and the 

nitrogen removed by certain crops. cornell 

lysi meter tanks. 



Soils 


CaO 

% 


N 
% 


Pounds of N Removed 
PER Acre 


MAIZE 
1915 


OATS 

1916 


BARLEY 
1917 


Dunkirk silty clay loam. . . 
First foot 


.340 

.280 

.490 

1.530 

.230 
.165 
.260 
.365 


.134 
.062 
.064 
.054 

.145 
.052 
.059 
.050 


53.6 

28.3 


62.3 
21.7 


44.0 


Second foot 




Third foot 




Fourth foot 




Volusia silt loam 


18.8 


First foot 




Second foot 




Third foot 




Fourth foot 













and in a general way there is often some correlation between 
the amount of calcium present and the productivity. In 
humid regions soils high in lime are usually fertile. AVithin 
certain limits, therefore, calcium becomes significant in fer- 
tility studies.^ 

Some idea concerning the relative value of the various chem- 
ical methods, especially those dealing with potash, lime, phos- 
phoric acid, and magnesia, may perhaps be obtained by com- 
paring actual data. Burd - has analyzed a number of soils, 



^Shedd, O. M., A Proposed Method for the Estimation of Total 
Calcium in Soils and the Significance of this Element in Soil Fertility; 
Soil Sci., Vol. X, No. 1, pp. 1-14, 1920. 

* Burd, J. S., Chemical Criteria, Crop Production and Physical Classi- 
fication in Two Soil Classes; Soil Sci., Vol. V, No. 6, pp. 405-419, 1918. 



326 



NATURE AND PROPERTIES OF SOILS 



some good, some poor, by several different methods. Repre- 
sentative figures are given below : 

Table LXXIV 

chemical composition of a good and a poor soil as 
indicated by several different methods 



Conditions 


Percentage of 




K,0 


CaO 


MgO 


P.O. 


Bulk analysis 

Productive silt loam 


1.98 
1.85 

1.05 

.89 

.039 
.039 

p.p.m. 

57 

52 


1.48 
1.50 

1.43 
1.48 

.452 

.422 

p.p.m. 

127 

45 


2.66 
3.57 

2.46 
3.32 

.220 
.144 

p.p.m. 

40 
23 


.23 


Unproductive silt loam 

Concentrated HCl digestion 
Productive silt loam 


.21 
.22 


Unproductive silt loam 

One per cent, citric acid 

Productive silt loam 


.20 
.101 


Unproductive silt loam 

Water extract 

Productive silt loam 


.072 

p.p.m. 
12 


Unproductive silt loam 


5 



A comparison of the figures from the good and poor soil 
seems to indicate no differences large enough to warrant opin- 
ions regarding their relative fertility, except in the case of the 
water extracts. These latter figures, however, are seasonal 
averages and required as long a time to procure as was neces- 
sary to grow a crop. Such fertility measurement is not as 
practicable as actually using the crop as an indicator. 

172. Resume. — The conclusion that chemical analyses are 
of but little direct practical value as a guide to soil prod- 
uctivity is unavoidable. In spite of the great importance of 
chemistry in research and teaching, it fails to indicate either 
the permanent or the immediate fertility of the land. No 
chemical method is capable of showing substantial and con- 
stant differences between soils producing within 20 per cent. 



CHEMICAL ANALYSIS OF SOILS 327 

of each other. Even if an analysis should show the nutrients, 
which would be available over a term of years, it would still be 
inadequate, since available nutrients are only one of a great 
number of factors which govern productivity.^ This produc- 
tivity equation may be indicated as follows : 

Productivity := Texture X structure X organic matter X 
moisture X available nutrients X soil reaction X weather X 
plant disease X care of farmer, etc., etc. 

The factors of this equation are variables, their importance 
in determining productivity depending on many things. An 
accurate knowledge of the available soil nutrients, even if 
procurable, would aid but little in solving such an equation. 

The solution of individual or community fertility problems 
is best accomplished by the aid of experienced and technically 
trained men, who understand the scientific principles under- 
lying the common field procedures and who also are in touch 
with the experiences of farmers over wide and diverse areas. 
Such men may advise not only in regard to the crops that 
should be grown but also as to their rotation, management, 
and fertilization from seeding until harvest. These men may 
also institute such cooperative experiments and tests as will 
best throw, light on fertility problems untouched by practical 
experience. 

* The samples sent to a chemical laboratory by farmers are gen- 
erally improperly taken and consequently are not representative. It 
would be unwise to analyze such soils even if the methods were capable 
of showing all that could be wished for. 



CHAPTER XVII 
'ALKALI SOILS ^ 

It has already been shown that soils are acted on by a ^eat 
variety of weathering agents which gradually render soluble 
a portion of the most susceptible constituents. This soluble 
material becomes a part of the soil solution and may come in 
contact with the roots of any crop growing on the land. In 
humid regions, where a large quantity of water percolates 
through the soil, this soluble matter has little opportunity to 
accumulate.^ In arid regions, however, where loss by drainage 
is slight, these salts may often collect in large amounts. Dur- 
ing periods of dry weather they are carried upward by the 
capillary rise of the soil-water, while during periods of rain- 
fall they may move downward again in proportion to the leach- 
ing action. At one time the lower soil may contain consid- 
erably more soluble salt than the upper; at another time the 
condition may be reversed, in which case the solution in con- 
tact with roots may contain so much soluble matter that vege- 
tation is injured or destroyed. This excess of soluble salts 
usually has a marked alkaline reaction, but in any case it pro- 
duces what is termed an alkali soil. 

Large areas of land in every continent carry soluble salts 
to such an extent that alkali injury is either actual or poten- 

* For a complete and satisfactory treatise on alkali see Harris, F. S., 
Soil Alkali, New York, 1920. 

^ Peat soils in humid regions may sometimes contain high concentra- 
tions of salts, commonly non-toxic, and lower concentrations of ex- 
tremely toxic salts. 

Conner, S. D., Excess Soluble Salts in Humid Soils; Jour. Amer. Soc. 
Agron., Vol. 9, No. 6, pp. 297-301, 19 17. 

328 



ALKALI SOILS 329 

tial. It is estimated that 13 per cent, of the irrigated land of 
the United States contains sufficient soluble salts seriously to 
interfere with crop growth. This. alone amounts to nine mil- 
lion acres and does not include the millions of acres not under 
the ditch that are affected to a marked degree by alkali. Sim- 
ilar figures are available from other continents and, since 
alkali conditions can be alleviated and controlled to a certain 
extent, the importance of the subject becomes apparent. 

Entirely aside from the economic aspects, alkali is of great 
interest scientifically, offering a research field of such range 
and complexity as to involve many sciences. A greater por- 
tion of the practical information regarding alkali and its con- 
trol has arisen from the purely scientific interest that has 
been directed towards this peculiar soil condition. 

173. Composition of alkali. — It has been emphasized pre- 
viously that the solution of a normal humid-region soil is of 
such dilution as to be largely ionic in character except in 
periods of low moisture content. In a soil affected with 
alkali it is obvious that the molecular state is dominant and 
that certain salts may exist and function as definite entities. 
Thus the following bases may be expected to be present — 
sodium, potassium, magnesium, calcium, and sometimes am- 
monium. The common acid radicals are chlorides, sulphates, 
carbonates, bicarbonates, phosphates, and nitrates. The salts 
that are present and their proportion not only in the soil solu- 
tion but as a precipitant will vary with conditions. 

The following table indicates not only the salts that may be 
present but the composition of the alkali as reported by a 
number of different investigators. (See table LXXV, p. 330.) 

174. White and black alkali. — Sulfates and chlorides of 
the alkalies, when concentrated on the surface of the soil, 
produce a white incrustation, which is very common in alkali 
regions during a dry period as a result of the evaporation of 
moisture. Incrustations of this character are called white 
alkali. 



330 NATURE AND PROPERTIES OF SOILS 

Table LXXV 

comparison of alkali expressed in percentage of the dif- 
ferent salts present. 





>^ 


California 
(Tulare) 
Exp. Sta.^* 


Yakima,^ 
Wash. 
12-24 
Inches 


PiLLiNGS, Mont.' 


Yuma, Ariz.' 


Salt 


Crust 


Surface 

10 
Inches 


Crust 


0-72 
Inches 


KCl 

K^SO, 

K.CO3 

Na^SO^.... 

NaN03 

Na2C03.... 

NaCl 

Na.HPO^... 

MgSO, 

MgCl, 

CaCL 

NaHCOg... 

CaSO, 

Ca(HC03), 
Mg(HC03); 
(NHJ3CO3 


1.6 

33.1 
6.6 

12.7 
17.3 

21.5 


3.9 

25.3 
19.8 
32.6 
14.7 

2.2 

1.4 


5.6 
9.7 

13.8 

36.7 

1.9 

16.5 

15.7 


1.6 

85.6 

.5 

8.9 

.6 

2.7 


21.4 

35.1 

7.3 

4.0 

22.0 
10.0 


4.0 

81.1 

7.7 
.2 
.3 

6.6 


22.0 

13.7 

6.9 
4.0 

21.0 
32.2 



Carbonates of the alkalies, particularly sodium carbonate, 
dissolve organic matter from the soil, thus giving a dark color 
to the solution and to the incrustation. For this reason, alkali 
containing large quantities of these salts is called tlack alkali. 
Black or brown alkali may also be produced by calcium chlo- 
ride or by an excess of sodium nitrate. 

Black alkali is much more destructive to vegetation than is 
the white. A quantity of the latter which would not seriously 

^Headden, W. P., The Fixation of Nitrogen; Colo. Agr. Exp, Sta., 
Bui. 155, p. 10, 1910. 

' Hilgard, E. W., Soils, p. 442, New York, 1906. 

'Dorsey, C. W., Alkali Soils of the United States; U. S. Dept. Agr., 
Bur. Soils, Bui. 35, 1906. 



ALKALI SOILS 331 

interfere with the growth of most crops might completely pre- 
vent the development of useful plants if the alkali were black. 

175. Origin of alkali. — While the presence of alkali and 
its influence on plants has been known for centuries, it is 
only within recent years that its probable mode of origin has 
been understood. The soluble salts have undoubtedly come 
from the materials which have formed the soils, the reactions 
being as complex as the ordinary transformations which take 
place in soil formation. 

Some soils have been laid down as deltas in arms of the 
ocean. If these bodies of water later are cut off from the sea 
and gradually dry up under arid conditions, an alkali soil 
will be left. In a similar way saline lakes may disappear and 
soils heavily charged with alkali will result. 

The commonest mode of origin for alkali soil is through 
ordinarj^ weathering under conditions of aridity. Almost any 
rock will give rise to soils rich in alkali salts if leaching is not 
a feature in the weathering processes. In western United 
States the origin of much of the soil affected to the greatest 
degree with alkali is associated with strata originally carrying 
much soluble material. When such rock forms soil, the alkali 
arises not only from the decomposition of the minerals of 
which the rock is composed, but is greatly reinforced by the 
soluble salts already present. The Cretaceous and Tertiary 
beds in Utah, Colorado, and Wyoming are of this character, 
having been laid down in brackish water. They naturally 
give rise to soils high in alkali.^ 

One fact that is often overlooked in practice is that the 
amount of alkali in the surface layers of soil may be greatly in- 
creased by improper handling. Rapid evaporation after rain 
or irrigation will carry the soluble salts toward the surface and 
deposit them near to or in the root zone. Again, over-irriga- 

^ Stewart, R., and Peterson, W., Origin of Alkali; Jour. Agr. Res., 
Vol. X, No. 7, pp. 331-353, 1917. See also, Breazeale, J. F., Forma- 
tion of Black Alkali in Calcareous Soils; Jour. Agr. Res., Vol. X, No. 
11, pp. 541-589, 1917. 



332 NATURE AND PROPERTIES OF SOILS 

tion may produce leaching into lower lands, an alkali condition 
generally resulting if the areas so affected remain water-logged 
for a long time. 

Very often alkali is localized in small areas called alkali 
spots. These vary in size from a few square yards to several 
acres. In years of good rainfall these areas may be pro- 
ductive, but in dry years they are often quite sterile. Their 
origin is generally due to seepage, the ground water being 
near enough the surface to allow a concentration of salts by 
capillarity, especially in dry seasons. 

A very peculiar type of alkali spot occurs in the Grand 
Valley of Colorado and elsewhere, the predominant salt being 
the nitrate, which does not usually occur in large amounts 
as alkali. Two theories have been advanced to account for the 
presence of the nitrate salts. One hypothesis ^ is that the 
surrounding shales are comparatively rich in nitrates and that 
the alkali accumulation is a leaching and seepage process. The 
other theory is biological in nature.^ Such soils are capable 
of rapid nitrogen fixation by means of their bacterial flora. 
The idea is advanced that the nitrogen is fixed from the air 
very rapidly in these spots and later oxidized to the nitrate 
form. Whatever the origin of the soluble salts the fact re- 
mains that such spots are quite destructive, spreading very 
rapidly until whole orchards are wiped out. 

Water used for irrigation is very often heavily charged with 
alkali, especially where any amount of the water previously 
applied to the soil finds its way back into the streams. At 
Canon City, Colorado, the Arkansas River is very pure. At 
a point 120 miles below the soluble salts have been known 

^ Stewart, E., and Peterson, W., The Nitric Nitrogen Content of the 
Country Eock ; Utah Agr. Exp. Sta., Bui. 134, 1914. 

Also, Further Studies of the Nitric Nitrogen Content of the Country 
Bock; Utah Agr. Exp. Sta., Bui. 150, 1917. 

" Headden, W. P., The Fixation of Nitrogen in Colorado Soils; Colo. 
Agr. Exp. Sta., Bui. 186, 1913. 

Sackett, W. G., and Isham, R. M., Origin of the Niter Spots in 
Certain Western Soils; Science, N. S., Vol. 42, pp. 452-453, 1915. 



ALKALI SOILS 



333 



to reach a concentration of 2200 parts per million. The quan- 
tity of soluble salts that may be present in irrigation water 
before it is unfit for use depends on certain conditions. This 
amount will vary with the crop, the rainfall, the soil, the 
composition of the alkali, and a number of other factors. 



^ 
^ 
^ 



I 



Fig. 54. — Diagram showing the amount and composition of alkali salts 
at various depths in a soil at Tulare, California. (After Hilgard.) 



.45 




























A 






.35 












\ 
















V 

V; 


\ 




.Jo 












^ 


C 
(i 




.£^ 


















.£0 
./3 










/ /?Z-/ 




■1 








^ 


/^ 






V 




.05 






/ 






(S 


^^C 


^ 






U-- 


^-<rl 


"'^-y 


^ 




.e._\ 


O 




/ 




c. 


7 


^ 


; 


4 



Where the alkali is of the sodium sulfate type rather high 
concentrations are admissible, running as high as 1000 parts 
per million. Water carrying black alkali must be used with 
great caution. Table LXXVI indicates the concentration that 
may be expected in normal irrigation water. 

The preponderance of sodium chloride is almost always a 
feature, not only in alkali water but also in soils affected with 
alkali salts. This may be explained as due to differential ab- 



334 NATURE AND PROPERTIES OF SOILS 



Table LXXVI 

analysis of some typical alkaline river water of western 
united states.^ 



Stream 


Total 
Solids 
p.p.m. 


Percentage of Total Solids as 




CI 


SO, 


CO3 


Na 


K 


Ca 


Mg 


SiO, 


Malad River, Utah .... 
Sevier River at Delta, 

Utah 

Rio Grande, Texas 

Mill Creek, Montana . . 
San Benito, California. 
Buckeye Canal, Arizona 


4,395 

1,316 
791 

3,747 
936 

1,972 


50.0 

25.0 
21.6 
7.4 
13.8 
39.9 


2.9 

24.1 
30.1 
17.3 
29.0 
7.3 


4.7 

17.9 
11.5 
35.1 
38.3 
9.6 


37.4 

16.4 
14.8 
23.5 
13.1 
24.9 


".8 
1.4 
5.4 

.6 


5.3 

13.7 

10.1 

6.6 

6.6 


6.5 
3.0 

2.2 
7.7 
2.9 


sis 

.7 
2.6 

2.7 



sorption of ions by the soil. Sodium and chlorine ions seem 
to be about as little absorbed by the soil as any of the com- 
mon soil constituents. They are thus readily carried through 
the soil and are free to accumulate in considerable amounts 
at points where they may become noticeable. Their union of 
necessity produces large quantities of sodium chloride or com- 
mon salt.^ 

176. Effect of alkali on crops. — The presence of rela- 
tively large amounts of salts dissolved in water and brought 
into contact with a plant cell has been shown to cause a shrink- 
age of the protoplasmic lining of the cell. This action, called 
plasmolysis, increases with the concentration of the solution 
until the plant finally dies. The phenomenon is due to the 
osmotic movement of the water, which passes from the cell 
towards the more concentrated soil solution. The nature of the 
salt, the species, and even the individuality of the plant, as 
well as other factors, determine the exact concentration at 
which the plant succumbs. The carbonates of the alkali bases 
have, in addition, a corroding effect on the plant tissues, dis- 

^ Harris, F. S., Soil AllcaU, p. 232; New York, 1920. 
' Dorsey, C. W., Alkali Soils of the United States; U. S. Dept. Agr., 
Bur. Soils, Bui. 35, 1906. 



ALKALI SOILS 



335 



solving the parts of the plant with which they come into con- 
tact. Such action is not as important as i)lasmolysis and when 
it does occur is most noticeable at the root crown. (See 
Fig. 55.) 

Indirectly, alkali may influence plants by its effect on soil 
tilth, soil organisms, and fungous and bacterial growths. Mar- 
chal,^ for example, found that the formation of nodules, con- 
taining the nitrogen-fixing organisms, did not develop well 




Fig. 55. — '(1) Cross-section diagram of a normal plant cell, 
after plasmolysis has taken place. 



(2) Cell 



on pea roots in nutrient solutions when certain concentra- 
tions of salts were maintained. Ammonium salts were injuri- 
ous at a concentration of 500 parts per million. Potassium and 
sodium salts retarded the nodule development at 5000 and 3333 
parts to the million respectively. The quantity of alkali that 
will cause injury to ammonifying and nitrifying bacteria 
varies from 250 to 4000 parts per million, depending on con- 
ditions. 

177. Resistance of different plants to alkali. — The fac- 
tors that determine the tolerance of plants toward alkali are : 

^ Marelial, E., Influence des Sels minermtx nv.tritifs sur la Production 
des nodosites chez le Pois; Compt. Eend. Acad. Sci. (Paris), Tome 133, 
No. 24, p. 1032, 1901. 



336 NATUEE AND PROPERTIES OF SOILS 

(1) the physiological constitution of the plant, and (2) the 
rooting habit. The former is little understood, so much de- 
pending on the character of the alkali solution, the nature 
of the cell-wall, and the character and activity of the cell con- 
tents. It has long been known that the toxicity of two salts 
when together is considerably less than the sum of their detri- 
mental action when used alone. This ameliorating or antagon- 
istic action varies for different salts, seeming to be greatest 
when calcium and magnesium are involved. This is but an 
example of the complexities which arise when an attempt is 
made to study the physiological relationships of alkali injury. 

The rooting habit of plants in their relation to alkali toler- 
ance is more easily understood. The advantage is always with 
deep-rooted crops, such as alfalfa and sugar-beets, probably 
because a portion of the root may be in a less strongly impreg- 
nated part of the soil. 

The tolerance of many plants to alkali has been studied in 
water culture. Such results are not of great practical value, 
however, as it is only in soil that all of the numerous factors, 
such as absorption, antagonism, and physical conditions, come 
into play. Harris and Pittman ^ found that organic matter 
in a soil had a marked ameliorating influence on alkali injury, 
especially from sodium carbonate. High moisture was also an 
important factor in lowering the toxicity of soluble salts. 

Guthrie and Helms,^ using a rich garden loam, found the fol- 
lowing concentrations slightly affecting or entirely preventing 
germination and growth of certain crops. (Table LXXVII.) 

Of the cereals, barley and oats are the most tolerant, these 
being able, in some cases, to produce good crops in soil con- 
taining two-tenths per cent, of white alkali. Of the forage 
crops, a number of valuable grasses are able to grow on soil 

^ Harris, F. S., and Pittman, D. W., Soil Factors Affecting the 
Toxicity of Alkali; Jour. Agr. Res., Vol. XV, pp. 287-319, 1918. 

' Guthrie, F. B., and Helms, E., Pot Experiments to Determine the 
Limits of Endurance of Different Farm Crops for Certain Injurious Sub- 
stances; Agr. Gaz., N. S. Wales, Vol. 14, No. 2, pp. 114-120", 1903. 



ALKALI SOILS 



337 



Table LXXVII 

effect of certain concentrations of salts on crops, 
pressed in parts per million. 



EX- 





NaCl 


Na^COa 




Wheat 


Barley 


Eye 


Wheat 


Barley 


Eye 


Germination affected. 
Germination prevented 

Growth affected 

Growth prevented. . . . 


500 
2000 

500 
2000 


1000 
2500 
1000 
2000 


1000 
4000 
1500 
2000 


3000 
5000 
1000 
4000 


2500 
6000 
1500 
4000 


2500 
5000 
2500 
4000 



containing considerably more than two-tenths per cent of al- 
kali. Timothy, smooth brome, and alfalfa are the cultivated 
forage plants most tolerant of alkali, although they do not 
equal the native grasses in this respect. Cotton also tolerates 
a considerable amount of alkali. 

Loughridge,^ after experiments and observation for a num- 
ber of years, has obtained data regarding the resistance of 
various crops to the several alkali salts. His results are given 
in part as follows, expressed in pounds to an acre to a depth of 
four feet. ( See table LXXVIII, page 338. ) 

Although in general the results as to the resistance to alkali 
of the various crops are so conflicting, the Bureau of Soils,^ 
in its alkali mapping, has been able to make a rough classifi- 
cation as follows, (See table LXXIX, page 338.) 

178. Conditions that influence the effect of alkali. — It 
has already been mentioned that organic matter and a high 
moisture content of the soil tended to alleviate alkali toxicity. 
Should, however, a previously wet soil become dry, the solu- 
tion, originally very dilute, would become concentrated and 

* Loughridge, E. H., Tolerance of AlMli hy Various Cultures; Calif, 
Agr. Exp. Sta., Bui. 133, 1901. See also Kearney, T. H., and Harter, 
L. L., Comparative Tolerance of Various Plants for the Salts Com- 
mon in AR-ali Soils; U. S. Dept. Agr., Bur. Plant Ind., Bui. 113, 1907. 

» Dorsey, C. W., All-ali Soils of the United States; U. S. Dept. Agr., 
Bur. Soils, Bui. 35, pp. 23-25, 1906. 



338 



NATURE AND PROPERTIES OF SOILS 



Table LXXVIII 



Crop 



Grapes. . . . 
Oranges. . . 

Pears 

Apples. . . . 
Peaches. . . 

Rye 

Barley .... 
Sugar Beet 
Sorghum. . 
Alfalfa.... 
Saltbush. . . 



Na2S04 



40,800 

18,600 

17,800 

14,240 

9,600 

9,800 

12,020 

52,640 

61,840 

102,480 

125,640 



Na^COa 



7,550 

3,840 

1,760 

640 

680 

960 

12,170 

4,000 

9,840 

2,360 

18,560 



NaCl 



9,640 
3,360 
1,360 
1,240 
1,000 
1,720 
5,100 
5,440 
9,680 
5,760 
12,520 



Total 
Alkali 



45,760 
21,840 
20,920 
16,120 
11,280 
12,480 
25,520 
59,840 
81,360 
110,320 
156,720 



consequently toxic. High moisture should, therefore, bie 
maintained at least as long as the crop is upon the soil. 

The distribution of the alkali at different depths may have 
an important bearing as to its effect on plants. Young plants 
and shallow-rooted crops may be entirely destroyed by the 
concentration of alkali at the surface, while the same quantity 
evenly distributed through the soil, or carried by moisture to 
a lower depth, would have caused no injury. A loam soil, by 



Table LXXIX 



Percentage of 


Percentage of 




Total Salts in 


Black Alkali 


Crops 


Soil 


IN Soil 




.00— .20 


.00— .05 


All crops grow 


.20— .40 


.05— .10 


All but most sensitive 


.40 .60 


.10— .20 


Old alfalfa, sugar beet, sorghum, 
barley 


.60—1.00 


.20— .30 


Only most resistant plants 


1.00—3.00 


above .30 


No plants 



ALKALI SOILS 339 

reason of its greater water-holding capacity and absorptive 
power, will contain more alkali without injury to plants than 
will a sandy soil. Certain of the alkali salts exert a deflocculat- 
ing action on clay soils and effect an indirect injury in that 
way. 

In irrigated regions the injurious effects of alkali are in 
many cases developed only after irrigation has Been practiced 
for a few years. This is due to what is known as a "rise of 
alkali" and comes about through the accumulation, near the 
surface of the soil, of salts that were formerly distributed 
throughout a depth of perhaps many feet. Before the land 
was irrigated the rainfall penetrated only a slight depth into 
the soil, and when evaporation took place salts were drawn to 
the surface from only a small volume of soil. When, however, 
irrigation water is turned on the land, the soil becomes wet to 
a depth of perhaps fifteen or twenty feet. During the por- 
tion of the year in which the soil is allowed to dry large quan- 
tities of salts are carried toward the surface by the upward- 
moving capillary water. 

Although these salts are in part carried down again by the 
next irrigation the upward movement constantly exceeds the 
downward one. This is because the descending water passes 
largely through the non-capillary interstitial spaces, while the 
ascending water passes almost entirely through the capillary 
channels. The smaller spaces, therefore, contain a consider- 
able quantity of soluble salts after the downward movement 
ceases and the upward movement begins. In other words, the 
volume of water carrying the salts downward in the capil- 
lary spaces is less than that carrying them upward through 
these spaces. Surface tension causes the salts to accumulate 
largely in the capillary spaces, and it is, therefore, the direc- 
tion of the principal movement through these spaces that de- 
termines the point of accumulation of the alkali. 

There are large areas of land in Eg\'pt, in India, and even 
in France and Italy, as well as in this country, that have suf- 



340 NATURE AND PROPERTIES OF SOILS 

fered in this way, and not infrequently they have reverted 
to a desert state. 

179. Alkali vegetation. — There are a great number of 
plants that seldom grow on soils other than those affected with 
alkali. Davy ^ states that there are 197 species restricted to 
alkali soils in California. Such plants are generally recog- 
nized by the farmers in the district as indicators of alkali. 
Care should be taken, however, in thus classifying alkali land. 
Such plants should occupy the land to the exclusion of less 
tolerant species. Some of the plants ^ whose presence should 
cause one to surmise alkali conditions are as follows : 

Greasewood Inkweed 

Alkali-heath Tussock-grass 

Salt-grass Bushy samphire 

Salt-bush Spike-weed 

Cressa Rabbit bush 

Sage-brush, which is so often associated in popular literature 
with alkali, does not grow on land which carries a great amount 
of soluble salts. In locating land it is, therefore, a good indi- 
cator of alkali-free conditions, especially if it is growing vig- 
orously. 

180. The handling of alkali lands.^ — Ordinarily there 
are two general ways in which alkali lands may be handled in 
order to avoid the injurious effects of soluble salts. The first 
of these is eradication, the second may be designated as con- 
trol. In the former case an attempt is made actually to elimi- 

^ Davy, J. B.j Investigations on the Native Vegetation of Allcali 
Lands; Calif. Exp. Sta. Eep., 1895-97, pp. 53-75. 

' Harris, F. S., Soil Alkali; Chap. VI,* New York, 1920. 

' Dorsey, C. W., Beclamation of Alkali Soils; U. S. Dept. Agr., Bur. 
Soils, Bui. 34, 1906. Also, Hilgard, E. W., Utilisation and Beclamation 
of Alkali Soils; New York, 1911. Also, Brown, C. F., and Hart, E, A., 
Beclamation of Seeped and Alkali Lands; Utah Agr. Exp. Sta., Bui. Ill, 
1910. Also, Dorsey, C. W., Beclamation of Alkali Soils at Billings, 
Montana; IT. S. Dept. Agr., Bur. Soils, Bui. 44, 1907. Also Harris, 
F. S., Soil Alkali; Chaps. XII, XIII and XIV; New York, 1920. 



ALKALI SOILS 341 

nate by various means some of the alkali. In the latter, meth- 
ods of soil management are employed which will keep the salts 
well distributed throughout the soil. In many cases soils 
would grow excellent crops if the alkali could only be kept 
well distributed through the soil layers so that no concentra- 
tion that is toxic could occur, at least within the root zone. 
In general, steps should be taken toward the control of alkali, 
whether eradication is attempted or not. Under irrigation, 
careful attention is always wise. 

181. Eradication of alkali. — Of methods designed at 
least partially to free the soil of alkali the commonest are: 
(1) leaching with under-drainage, (2) correction with gyp- 
sum, (3) scraping, and (4) flushing. Of the various methods 
for removing an excess of soluble salts, the use of tile drains 
is the most thorough and satisfactory. When this method is 
used in an irrigated region heavy and repeated applications 
of water must be made, to leach out the alkali from the soil 
and drain it off through the tile. When used for the ameliora- 
tion of alkali spots in a semi-arid region, the natural rainfall 
will often in time effect the removal. 

In laying tiles it is necessary to have them at such a depth 
that the soluble salts in the soil beneath them will not readily 
rise to the surface. This will depend on those properties of the 
soil governing the capillary movement of water. Three or 
four feet in depth is usually sufficient, but the capillary move- 
ment should first be estimated. 

After the drains have been placed the land is flooded with 
water to a depth of several inches. The water is allowed to 
soak into the soil and to pass off through the drains, leaching 
out part of the alkali in the process. Before the soil has 
time to become very dry the flooding is repeated, and the 
operation is kept up until the land is brought into a satis- 
factory condition. 

Crops that will stand flooding may be grown during this 
treatment, and they will serve to keep the soil from puddling. 



342 NATURE AND PROPERTIES OF SOILS 

as it is likely to do if allowed to become dry at the surface. 
If crops are not grown, the soil should be harrowed between 
floodings. The operation should not be carried to a point 
where the soluble salts are reduced below the needs of the 
crop.^ The use of gypsum on black alkali land has sometimes 
been practiced for the purpose of converting the alkali carbon- 
ates into sulfates, thus ameliorating the injurious properties 
of the alkali without decreasing the amount. The quantity 
of gypsum required may be estimated from the amount and 
composition of the alkali. The soil must be kept moist, in 
order to bring about the reaction, and the gypsum should be 
harrowed into the surface, not plowed under. The reaction 
is as follows: 

NaXOa + CaSO, ^ CaCOg + Na.SO^ 

When soil containing black alkali is to be tile-drained, it 
is recommended that the land should first be treated with gyp- 
sum, as the substitution of alkali sulfates or carbonates causes 
the soil to assume a much less compact condition and thus fa- 
cilitates drainage. It also prevents the loss of organic matter 
dissolved by the carbonate of soda and the soluble phosphates, 
both of which are precipitated by the change. 

Removal of the alkali incrustation that has accumulated at 
the surface is sometimes resorted to. Very often the rise of 
alkali is encouraged by applications of irrigation water, which 
is allowed to evaporate unretarded. The salts are thus carried 
upward by the capillary movement of the soil-water. This 

* It has been suggested that elemental sulfur could be used to advan- 
tage in alkali land, especially where carbonates and bicarbonates abound. 
Sulfur generally oxidizes in the soil quite readily, producing an acid 
[see par. 221]. Instead of trying to remove all of the alkalinity by 
leaching, it might be more practicable to add sulfur. 

Lipman, J, G., Sulfur on Alkali Lands; Soil Sci., Vol. II, No. 3, 
p. 205, 1916. 

Hibbard, P. L., Sulfur for Neutralising Alkali Soil; Soil Sci., Vol. 
XI, No. 5, pp. 385-387, 1921. 



ALKALI SOILS 343 

method of alkali eradication is never very efficient, and is often 
dangerous, as it encourages the presence of very large amounts 
of alkali salts in the surface soil. 

Often alkali accumulations may be washed from the soil sur- 
face by turning on a rapidly moving stream of water. The tex- 
ture of the soil, as well as the slope of the land, must be just 
right for such a procedure. Generally so much water enters 
the soil that the land remains heavily impregnated with alkali 
salts. Both this method and the previous, even if successful, 
are only temporary. Moreover, lands carrying so much alkali 
as to admit of either one of these procedures may be so heavily 
charged as never to yield to any form of either eradication 
or control. 

182. Control of alkali.— Where excessive amounts of 
soluble salts do not exist in a soil the control of the alkali with 
a view of keeping it well distributed in the soil column is the 
best practice. The retardation of evaporation is, of course, the 
main object in this procedure. The intensive use of the soil- 
mulch is, therefore, to be advocated, especially in all irrigation 
operations where alkali concentrations are likely to occur. 
Such a method of soil management not only saves moisture, but 
also prevents the excessive translocation of soluble salts into 
the root zone. This method of control is the most economical, 
the cheapest, and the one to be advocated on all occasions, no 
matter what may have been the previous means of dealing with 
the alkali situation. Certain soils that are strongly impreg- 
nated with alkali may be gradually improved by cropping with 
sugar-beets and other crops that are tolerant of alkali and 
that remove large quantities of salts. This is more likely to be 
efficacious where irrigation is not practiced. Certain crops, 
moreover, while somewhat seriously injured when young, are 
very resistant once their root systems are developed. A good 
example is alfalfa, the young plants being very tender while 
the mature ones are extremely resistant. Temporary eradica- 



344 NATURE AND PROPERTIES OF SOILS 

tion of alkali may allow such a crop to be established. Farm 
manure has been found especially useful in this respect.^ The 
crop once well established will then maintain itself in spite of 
the concentrations that may occur later. 

' Lipman, C. B., and Gericke, W. F., The Inhibition by Stable Manure 
of the Injurious Effects of Alkali Salts in Soils; Soil Sci., Vol. VII, 
No. 2, pp. 105-120, 1919. 



CHAPTER XVIII 
SOIL ACIDITY 

A CHEMICAL or physico-chemical viewpoint regarding the 
soil and its solution is essential in explaining many of the phe- 
nomena, especially those relating to higher plants and their 
nutrition. Since plants respond so markedly to their chemical 
environment, the importance of soil reaction has long at- 
tracted much attention. Two conditions are popularly recog 
nized in this respect — soil alkalinity or alkali and soil acidity. 
The former condition can only occur where soluble salts may 
concentrate in the soil and is confined largely to arid and semi- 
arid regions. Soil acidity, on the other hand, is common only 
in humid sections. So widespread is it occurrence and so 
marked is its influence on crop yields that its importance in 
a practical way surpasses that of soil alkali. 

183. General nature of soil acidity.^ — The nature of soil 
acidity is so little understood that it is impossible to define 
or explain it except in the most general terms. So-called soil 
acidity may be considered for practical purposes as a more 
or less unfavorable condition for plant growth, arising in the 
soil through a lack of certain active bases such as calcium and 
magnesium and which in practice is alleviated by the addition 
of some form of lime.^ 

Technically three reasons may be suggested as accounting 
for the harmful effects of soil acidity: (1) unfavorable hydro- 

* Maelntire, W. H., The Nature of Soil Acidity with Regard to its 
Quantitative Determination; Jour. Amer. Soc. Agron., Vol. 13, No. 4, 
pp. 137-161, 1921. 

^ Lime in an agricultural sense refers to all of the compounds of cal- 
cium and magnesium commonly utilized in correcting soil acidity. 

345 



346 NATURE AND PROPERTIES OF SOILS 

gen ion concentrations;^ (2) presence of substances harm- 
ful to plant growth such as active aluminum, manganese and 
the like, the presence of which is usually accompanied by a 
hydrogen ion concentration beyond neutrality; and (3) im- 
proper nutrition arising from a lack of calcium as a nutrient 
or as a synergistic agent in facilitating the entrance of other 
nutrient ions into the plant.- 

184. Hydrogen ion concentration. — A number of condi- 
tions are possible if the toxic influence of soil acidity is due to 
an actual acid. The harmful effect might be due to an ab- 
normally high hydrogen ion concentration arising from (1) 
soluble organic or inorganic acids in the soil solution. Again 
it might be due to (2) insoluble acids or acid salts which, on 
reaction with water, produce acidity. In this case, the hydro- 
gen ion concentration of the soil solution at any particular time 
would not be a measure of the so-called soil acidity.^ A harm- 
ful hydrogen ion influence may also be ascribed (3) to soluble 
acids, either organic or mineral, absorbed by the soil complexes 
and which would become active only under certain conditions. 
An additional feature of the actual acidity theory may lie in 
(4) the selective absorption of bases by the soil, by which acid- 
ity might be developed from neutral or even alkaline salts. 
If the actual acidity explanation is entertained, any one or all 
of these phases might be considered as contributing to the dele- 
terious effects so noticeable on certain plants. 

185. Active toxic bases. — The explanation of the harm- 
ful effects of so-called soil acidity as being due to the presence 
of active toxic bases has of late received much attention. The 

^Hydrogen is the one essential constituent of all acids. When dis- 
solved in water, acids dissociate, the hydrogen ion becoming active. The 
strength of an acid is determined by its hydrogen ion concentration. 

^ True speaks of this cooperative relationship as synergism. By it 
calcium makes other nutrients physiologically available. True, E. H., 
The Function of Calcium in the Nutrition of Seedlings; Jour. Amer. 
Soc. Agron., Vol. 13, No. 3, pp. 91-107, 1921. 

'Rice, F. E., and Osugi, S., The Inversion of Cane Sugar by Soils 
and Allied Substances and the Nature of Soil Acidity; Soil Sci., Vol. V, 
No. 5, p. 347, 1918. 



SOIL ACIDITY 347 

presence of active aluminum in so-called acid soils has been 
known for some time. Abbott, Conner, and Smalley ^ showed 
in 1913 that aluminum salts were the toxic agents in a certain 
unproductive soil. In 1918, Hartwell and Pember - proved 
quite definitely that, for certain soils and for certain crops, 
the aluminum ion was the injurious factor rather than the 
hydrogen ion that accompanied it. The work of Mirasol ^ indi- 
cates that active aluminum is usually present in acid soils.* 

Although soluble iron is seldom present to an excess, its 
ferrous salts are known to be toxic to a greater extent than 
acids of the same concentration.'' While soluble iron may ac- 
company active aluminum, it is questionable whether it ac- 
tually figures in acidity effects. The toxic influence of man- 
ganese is more probable, since it is more soluble in an acid than 
a neutral soil. While it is extremely toxic to plants above 
a certain concentration the recent work of Funchess " with 

' Abbott, J. B., Conner, S. D., and Smalley, H. E., Soil Acidity, Nitri- 
fication and the Toxicity of Soluble Salts of Aluminum; Ind. Agr. Exp. 
Sta., Bui. 170, 1913. 

'Hartwell, B. L., and Pember, F. R., The Presence of Aluminum as a 
Season for the Difference in the Effect of So-called Acid Soil on Barley 
and Bye; Soil Sci., Vol. VI, No. 4, pp. 259-277, 1918. 

'Mirasol, J. J., Aluminum as a Factor in Soil Acidity; Soil Sci., 
Vol. X, No. 3, pp. 153-193, 1920. 

* See also, Kratzman, E., Zur Physiologischen Wirkung der Aluminium 
Sals; auf die Pflanze ; Chem. Ztg., Jahrgang 38, S. 1040, 1914. 

Ruprecht, R. W., Toxic Effect of Iron and Aluminum Salts on Clover 
Seedlings; Mass. Agr. Exp. Sta., Bui. 161, 1915. 

Miyake, K., The Toxic Action of Soluble Aluminum Salts upon the 
Growth of the Bice Plant; Jour. Biol. Chem., Vol. 25, No. 1, pp. 
23-28, 1916. 

Conner, S. D., Liming in Its Belation to Injurious Inorganic Com- 
pounds in the Soil; Jour. Amer. Soc. Agron., Vol. 13, No. 3, pp. 113- 
124, 1921. 

■* Conner, S. D., Liming in Its Belation to Injurious Inorganic Com- 
pounds in the Soil; Jour, Amer. Soc. Agron., Vol. 13, No. 3, p. 114, 
1921. 

'Funchess, M. J., Acid Soils and the Toxicity of Manganese; Soil 
Sci., Vol. VIII, No. 1, p. 69, 1919. 

See also, Kelly, W. P., The Influence of Manganese on the Growth 
of Pineapples; Haw. Agr. Exp. Sta., Bui. 23, 1909. 

Skinner, J, J., and Reid, F. R., The Action of Manganese Under Acid 
and Neutral Soil Conditions; U. S, Dept. Agr., Bui, 441, 1916. 



348 NATURE AND PROPERTIES OF SOILS 

Alabama soils indicates that it is probably of minor importance 
as compared with aluminum. A toxic effect from magnesium 
is possible, especially if there is not enough calcium to prevent 
it from exerting a poisonous influence. The presence of alumi- 
num or iron in an active form is generally accompanied by a 
high hydrogen ion concentration due to hydrolysis/ which 
takes place readily in many soils. 

186. Lack of nutrients. — Less is known regarding this 
condition than of the two previously discussed. The lack of 
sufficient nutritive calcium in an acid soil has often been sug- 
gested.^ In addition, it may be possible that some plants re- 
quire more calcium and other bases for their metabolic proc- 
esses when growing on a so-called acid soil, due to the gen- 
eration of particular conditions within the cells. Plants like 
alfalfa absorb large amounts of calcium and may find an acid 
soil especially unfavorable on this account. 

True ^ has shown that the presence of calcium in consider- 
able amount is necessary when certain plants are growing in 
nutrient solution, that other nutrient ions may penetrate the 
plant cells. Potassium, for example, was but slightly absorbed 
even when present in large amounts, unless a certain concen- 

* Hydrolysis is a double decomposition in which one of the inter- 
acting substances is water. The water produces H+ and OH- ions, 
the former uniting with the non-metallic portion of the substance and 
the hydroxy! with the remainder. 

Active basic radicals give, with feeble acids in water, salts which 
are alkaline. Active acids and active bases give neutral salts. Active 
acids and less active bases yield salts which are acid in reaction. 

A feeble base and a feeble acid may produce a salt which is either 
acid or alkaline. Ammonium sulfide (NH4)2S in solution is alkaline, 
since the ammonium hydroxide which tends to form is more dissociated 
than the hydrogen sulfide which also is present. Aluminum silicaj;es in 
water hydrolize readily and since aluminum hydroxide is less dissociated 
than silicic acid, the hydrogen ions predominate over the hydroxyl ions 
and an acid reaction results. 

*See Truog, E., Soil Acidity: Its Belation to the Growth of Plants; 
Soil Sci., Vol. V, No. 3, pp. 169-195, 1918. 

Also, Soil Acidity: Its Belation to the Acidity of the Plant Juices; 
Soil Sci., Vol. VII, No. 6, pp. 469-474, 1919. 

^ True, E. H., The Function of Calcium in the Nutrition of Seed- 
lings; Jour. Amer. Soc. Agron., Vol. 13, No. 3, pp. 91-107, 1921. 



SOIL ACIDITY 349 

tration of calcium ions was provided. This relationship, 
spoken of as synergism, may be seriously interfered with by 
so-called soil acidity. 

187. The present status of the question. — Each of the 
general hypotheses which have been advanced to explain the 
detrimental influence of soil acidity has considerable plausible 
evidence in its support. Cane-sugar, which is inverted only 
in the presence of an acid, was found by Rice and Osugi ^ to 
be inverted in soils, even when the water extracts from these 
same soils were neutral or even alkaline. This seemed to indi- 
cate that the acidity was actual and was inherent with the soil 
mass rather than with the soil solution. This would also sug- 
gest the presence of insoluble or absorbed acids that might be 
liberated by hydrolysis, thus producing a harmful hydrogen 
ion concentration. Other equally valuable data are available 
on this phase of soil acidity. The work of Hartwell and Pem- 
ber ^ and of Mirasol,^ however, is even more conclusive in re- 
gard to aluminum as a toxic agent, especially as they studied 
the problem from the plant standpoint. 

Conner,* investigating the comparative influence of sulfuric 
acid and aluminum sulfate on plants, has obtained some in- 
teresting data corroborating the work of Hartwell and Pember. 
By comparing a given hydrogen ion concentration with the 
same hydrogen ion concentrations plus equivalent amounts of 
aluminum ions, he was able to demonstrate the greater toxicity 
of aluminum to barley and rye in water culture. Since soluble 
aluminum so often accompanies an unfavorable hydrogen ion 

* Rice, F. E., and Osugi, S., The Inversion of Cane Sugar by Soils 
and Allied Substances and the Nature of Soil Acidity; Soil Sei., 
Vol. V, No. 5, pp. 333-358, 1918. 

^Hartwell, B. L., and Pember, F. R., The Presence of Aluminum 
as a Reason for the Difference in the Effect of So-called Acid Soil on 
Barley and Eye; Soil Sci., Vol. VI, No. 4, pp. 259-277, 1918. 

' Mirasol, J. J., Aluminum as a Factor in Soil Acidity; Soil Sci., 
Vol. X, No. 3, pp. 153-193, 1920. 

* Conner, S. D., Liming in Its Relation to Injurious Inorganic Com- 
pounds in the Soil; Jour. Amer. Soc. Agron., Vol. 13, No. 3, pp. 113- 
124, 1921. 



350 



NATURE AND PROPERTIES OF SOILS 



concentration, the importance of aluminum in acidity cannot 
be avoided. 

Table LXXX 

relative weights of barley and rye grown in water cul- 
ture, the hydrogen ion concentration is ex- 
PRESSED IN Ph/ 



Treatment 



Check... 
H0SO4.. 

A1,(S0J 
H0SO4.. 

AL(SOJ 



H Ion 

CONCENTKA- 
TION PH 



6.3 
4.2 
4.2 
3.9 
3.9 



Eelative Weights 



Barley 



100 


100 


93 


95 


68 


65 


73 


65 


47 


55 



Eye 



The only conclusion possible at the present time is that 
there are probably several kinds of acidity and many degrees 
of the same acidity as far as toxic influences are concerned. 
Moreover, dissimilar plants seem to be affected differently by 
the same acidity, while the same plants respond diversely at 
different times. Hoagland ^ and others ^ have demonstrated 
that some plants grow better in a slightly acid medium, which 

^ The hydrogen ion concentration of an acid in solution is a measure 
of the dissociation of that acid and of its strength. The specific acidity 
of pure water is taken as 1, the number of grams of H+ ions to a liter 
being .0000001 or 10-'. The exponent of the power is taken as an erpres- 
sion of the acidity. Pure water has a Ph value of 7, which is approxi- 
mate neutrality. An acid solution containing 4000 times more H+ ions 
would have a Ph value of 3.4. 

^ Hoagland, D. E., Eelation of the 
the Nutrient Medium to the Growth 
Jour. Agr. Ees., Vol. XVIII, No. 2, pp. 

' Gillespie, L. J., The Reaction of 
Hydrogen ion Concentration; Jour. Wash. Acad. Sci., Vol. 6, No. 
pp. 7-16, 1916. 

Sharp, L. T., and Hoagland, D. E., Acidity and Adsorption in Soils 
as Meas-ured by the Hydrogen Electrode; Jour. Agr. Ees., Vol. VII, 
No. 3, pp. 123-145, 1916. 

Gillespie, L. J., and Hurst, L. A., Hydrogen-ion Concentration — Soil 
Type— Common Potato Scab; Soil Sci., Vol. VI, No, 3, pp. 219-236, 
1918. 



Concentration and Reaction of 
and Adsorption of the Plant; 
73-117, 1919. 

the Soil and Measurements of 

1, 



SOIL ACIDITY 351 

seems to indicate that the hydrogen ion concentration less 
than a Ph value of 7, so often reported in so-called acid soils, 
is concomitant with a toxic constituent or with malnutrition 
and is not in itself the harmful agent.^ This argument, how- 
ever, does not admit that the hydrogen ion is not in many 
cases the true explanation of the toxicity of certain acid soils, 
nor does it suggest that lack of nutrients may not be a serious 
consideration. 

In light of the explanations offered above, it is evident that 
the term soil acidity is inadequate to express the inorganic 
toxicity that accompanies a hydrogen ion concentration below 
Ph 7, as the condition referred to is, in many cases, not due to 
the hydrogen ion in detrimental concentration.- Since the 
term is of long standing and since so-called acid soils almost 
invariably yield an acid reaction with litmus paper, the phrase 
will continue in use in spite of its misleading inference. 

188. Why soil acidity develops.^ — No matter what hypoth- 

* Jofife found that while alfalfa plants experienced difficulty in becom- 
ing established in soils having high hydrogen ion concentrations due 
to the addition of sulfuric acidj once the seedlings became established 
they showed normal color and vigor and made excellent growth on soils 
having a Ph value as low as 3.8. 

Joflfe, J. S., The Influence of Soil Eeaction on the Growth of Alfalfa; 
Soil Sci., Vol. X, No. 4, pp. 301-307, 1920. 

^Researches on Danish soils extending from 1916 to 1920 show that 
the Ph value on different soils may vary from 3.4 to 8.0. A rather 
constant relationship was observed between the type of vegetation and 
the hydrogen ion concentration, many species being found only on 
soils within a certain range of Ph values. In water culture studies 
so-called acid-soil plants grew best at a Ph of about 4. Alkaline-soil 
plants seemed to give the strongest growth at a Ph of 6 to 7. 

Olseu, C, The Concentration of the Hydrogen Ions in the Soil; 
Science (N. S.), Vol. LIV, No. 1405, pp. 539-541, Dec. 2, 1921. 

'White, J. W., Studies in Acid Soils; Ann. Rep. Penn. State Col., 
1912-1913, pp. 55-104. 

Skinner, J. J., and Beattie, J. H., Influence of Fertilizers and Soil 
Amendments on Soil Acidity; Jour. Amer. Soc. Agron., Vol. 9, No. 
1, pp. 25-35, 1917. 

Conner, S. D,, Soil Acidity as Affected by Moisture Conditions of the 
Soil; Jour. Agr. Res., Vol. XV, No. 6, pp. 321-329, 1918. 

Martin, W. H., The Relation of Sulfur to Soil Acidity and to the 
Control of Potato Scab; Soil Sci., Vol. IX, No. 6, pp. 393-408, 1920. 



352 NATURE AND PROPERTIES OF SOILS 

esis may be considered as best explaining soil acidity, sci- 
entific and practical men are agreed that the addition of cer- 
tain compounds of calcium and magnesium tend to alleviate 
the detrimental condition. Conversely, almost every one is 
willing to admit that the most reasonable cause of its develop- 
ment is the loss or inactivity of certain bases. A lack of cal- 
cium seems especially prone to allow an increased hydrogen 
ion concentration to develop and may at the same time en- 
courage the activity of certain toxic bases or produce malnu- 
trition. The tendency of all soils in a humid region is, there- 
fore, towards acidity, their condition depending on the activ- 
ity of certain factors which seem to produce such a condition. 
The four important factors generally specified as encour- 
aging acidity are: (1) leaching losses, (2) cropping losses, 
(3) absorption phenomena within the soil, and (4) fertilizer 
residues. 

The loss of nutrient bases from the soil has already been 
emphasized (par. 163) and the importance of such removal is 
evident from the standpoint of plant nutrition. Over a period 
of ten years, the removal of nutrients from the Cornell lysi- 
meter soils,^ by drainage and rotation cropping together, 
amounted to 3702, 1741, and 942 pounds to the acre, respec- 
tively, for lime (CaO), potash (K2O), and magnesia (MgO). 
The loss of such amounts of bases cannot but permit the rapid 
development of soil acidity. No matter how well supplied 
the soil may be with favorable bases, it will in time become 
acid. 

Absorption, in its influence on soil acidity, produces its 
effect by rendering certain bases inactive rather than by 
removing them from the soil. When the activity of such bases 
as calcium is reduced by absorptive influences, not only does 
the hydrogen ion concentration of the soil solution tend to in- 
crease, but the hydrolysis of compounds carrying aluminum 
and similar bases seems to be encouraged. The acidity as de- 

* Unpublished data, Cornell Agr. Exp. Sta., Ithaca, N. Y. 



SOIL ACIDITY 353 

veloped may have a nutritive relationship as well as a toxic 
effect. 

When fertilizer salts are added to the soil, the basic ions 
are usually absorbed to a greater degree than the acid radi- 
cals. This tends to develop actual acidity in the soil solution, 
which may in itself be toxic or may facilitate the development 
of detrimental ions. If the crop utilizes the basic ion of the 
fertilizer added to a greater extent than the acid radical, it 
will aid in the development of acidity. If the plant, on the 
other hand, absorbs the acid radical, it will tend to counter- 
act the selective absorption by the soil. The combined influ- 
ences of soil and crop on ammonium sulfate tend to develop 
acidity, while the effect on sodium nitrate is toward alkalinity. 
A salt such as potassium nitrate should leave no residue. 

The decomposition of organic matter, especially when green- 
manures are plowed under, is often considered as increasing 
the acidity of the soil. Such may be the case at the beginning 
of the decomposition process, but the data ^ available on the 
subject seem to indicate that organic matter, if it exerts any 
influence on acidity, tends to reduce rather than accentuate 
it. This result may occur through the liberation of bases 
from the organic matter as decomposition proceeds. 

189. Relative tolerance of acidity by plants. — Since so 
many intermediate influences are possible in acid soils, and 
since plants respond so differently to these influences, it is im- 
possible to forecast the relative resistance of different crops 
on the same soil. The response of the same crop on differen"^ 
acid soils is likewise difficult to foretell. 

It is known that certain crops are often more tolerant to 
soil acidity than others. Of the common weeds sheep sorrel, 

^ White, J. W., Soil Acidity as Influenced by Green Manures; Jour. 
Agr. Ees., Vol. XIII, No. 3, pp. 171-197, 1918. 

Stephenson, E. E., The Effect of Organic Matter on Soil Reaction; 
Soil Sei., Vol. VI, No. 6, pp. 413-439, 1918. 

Howard, L. P., The Reaction of the Soil as Influenced by the De- 
composition of Green Manures; Soil Sci., Vol. IX, No. 1, pp. 27-38, 
1920. 



354 NATURE AND PROPERTIES OF SOILS 

paint-brush, daisy, and plantain seem especially resistant. 
This does not mean, however, that they grow better on an 
extremely acid soil than on one that is slightly acid or neutral. 
Some of the common crops that are tolerant of acidity are 
strawberry, blackberry, watermelon, red-top, Rhode Island 
bent-grass, cowpea, soybean, rye, millet, and buckwheat. Such 
crops as alfalfa, red clover, timothy, maize, oats, barley, cab- 
bage and sugar-beet seem to be susceptible in various degree 
to acid conditions. 

Reasons for the above differences are not as yet known, since 
plants apparently alike in every other respect differ in their 
reaction to the same acid condition. The following pairs of 
plants may be listed as examples: watermelon and musk- 
melon, blackberries and raspberries, apple and quince, turnip 
and beet, beans and alfalfa, red-top and timothy, rye and 
barley. The first of each pair mentioned will grow well on 
acid soils, while the second crop in each case is very detri- 
mentally affected.^ 

190. Tests for soil acidity.- — The great importance of 
soil acidity to plant growth has directed much attention 
towards methods for determining the acidity of the soil. 

^ Hartwell, B. L., Need for Lime as Indicated by Relative Toxicity of 
Acid Soil Conditions to Different Crops; Jour. Amer. Soc. Agron., Vol. 
13, No. 3, pp. 108-112, 1921. 

^Some of the important methods are compared and discussed in the 
following articles: 

Schollenberger, C. J., Eelation Between the Indications of Several 
Lime-requirement Methods and the Soil Content of Bases; Soil Sci., 
Vol. Ill, No. 3, pp. 279-288, 1917. 

Christensen, H. E., Experiments in Methods for Determining the 
Reaction of Soils; Soil Sci., Vol. IV, No. 2, pp. 115-178, 1917. 

Stephenson, K. E., Soil Acidity Methods; Soil Sci., Vol. VI, No. 1, 
pp. 33-52, 1918. 

Blair, A. W., and Prince, A. L., The Lime Requirement of Soils 
According to the Veitch Method, Compared with the Hydrogen-Ion 
Concentration of the Soil Extract; Soil Sci., Vol. IX, No. 4, pp. 253- 
259, 1920. 

Hartwell, B. L., Pember, F. E., and Howard, L. P., Lime Require- 
ment as Determined by the Plant and by the Chemist; Soil Sci., Vol. 
VII, Nc. 4, pp. 279-282, 1919. 



SOIL ACIDITY 355 

Such methods may be divided, for convenience of discussion, 
under two heads: quantitative determinations and qualita- 
tive tests. In the first case the methods devised purport to 
give the lime requirement of the -soil. The second group of 
methods attempts to determine whether the soil is acid and 
may in addition give some general idea as to the degree of 
acidity. 

191. Lime-requirement determinations. — A great num- 
ber of methods has been advanced for the determination of the 
lime requirement of soils. The methods may for convenience 
be grouped under three heads: (1) those using a neutral salt,^ 
(2) those utilizing a basic substance," and (3) miscellaneous 
procedures. 

In the first group, some neutral salt such as potassium ni- 
trate is added to the soil and the amount of actual acidity 
developed is determined under suitable control. The actual 
acidity produced by selective absorption and basic exchange 
is thus taken as a measurement of the soil acidity and is gen- 
erally figured to pounds of lime to the acre. 

In the second group some basic substance, preferably that 
which is used in practice to correct acidity, is added to the 
soil. The amount of the basic substance necessary to render 
the soil alkaline or neutral is determined in pounds to the 

* The Hopkins methods iitilize potassium nitrate or sodium chloride. 
Calcium acetate is used in the Jones method. 

Hopkins, C. G., Knox, W. H., and Pettit, J. H., A Quantitative 
Method for Betermininq the Aciditi/ of Soils; U. S. Dept. Agr., Bur. 
Chem., Bui. 73, pp. 114-121, 1903. 

Jones, C. H., Method for Determining the Lime Bequirement of 
Soils: Jour. Assoc. Off. Agr. Chemists, Vol. I, No. 1, pp. 43-44, 1915. 

^ The A^eitch method utilizes calcium hydroxide, the Tacke method 
calcium carbonate and the method proposed by Hutchinson and Mac- 
Lennan calcium bicarbonate. 

Veitch, F. P., Comparison of the Methods for the Estimation of 
Soil Acidity; Jour. Amer. Chem. Soc, Vol. 26, pp. 637-662, 1904. 

Tacke, Br., uber die Bestimmung der freien Humussduren ; Chem. 
Ztg., Bd. 21, Heft. 20, S. 174-175, 1897. 

Hutchinson, H. B., and MacLennan, K., The Determination of the 
Lime Bequirement of the Soil; Chem. News, Vol. 110, p. 61, 1914, 



356 NATURE AND PROPERTIES OF SOILS 

acre. Calcmm hydroxide and calcium carbonate are often 
used. 

Many investigators consider that the hydrogen ion concen- 
tration of the soil solution is a fair measure of the lime re- 
quirement of a soil.^ They thus assume that the concentra- 
tion of the hydrogen ion is a comparative indication of the 
amount of lime necessary to alleviate the detrimental influ- 
ences due to acidity. Bouyoucos - claims that the depression 
of the freezing point (see par. 145) may be used to measure 
soil acidity. He found that the depression of the freezing 
point was less for a neutral soil than for one either acid or 
alkaline. 

192. The Veitch method. — In order to show something 
of the procedure necessary in determining the lime require- 
ment of the soil, the Veitch method, which utilizes calcium 
hydroxide, will be briefly described. Eleven and and one-fifth 
grams of soil are placed in a suitable Erlenmeyer flask and 
treated with a standard lime-water solution. The amount of 
soil taken and the strength of the calcium hydroxide solution 
are such that each cubic centimeter of the latter absorbed by 
the soil indicates the need of 300 pounds of calcium oxide 
to the acre. A number of samples are run at the same time, 
receiving progressively larger amounts of lime-water. The 

^Gainey, P. L., Soil Reaction and Growth of Azotobacter; Jour. 
Agr. Ees., Vol. XIV, No. 7, pp. 265-271, 1918. 

Gillespie, L. J., and Hurst, L. A., Hydrogen Ion Concentration — 
Soil Type — Common Potato Scab; Soil Sci., Vol. VI, No. 3, pp. 219- 
236, 1918. 

Plummer, J. K., Studies in Soil Reaction as Indicated by the Hydro- 
gen Electrode; Jour. Agr. Res., Vol. XII, No. 1, pp. 19-31, 1918. 

Joffe, J. H., Hydrogen Ion Concentration Measurements in Soils in 
Connection with Their Lime Requirements ; Soil Sci., Vol. IX, No. 4, 
pp. 261-266, 1920, 

Blair, A. W., and Prince, A. L., The Lime Requirement of Soils 
According to the Veitch Method Compared with the Hydrogen Ion Con- 
centration of the Soil Extract; Soil Sc\, Vol. IX, No. 4, pp. 253-259, 
1920. 

=* Bouyoucos, G. J., The Freezing Point Method as a New Means of 
Determining the Nature of Acidity and Lime Requirements of Soils; 
Mich. Agr. Exp. Sta., Tech. Bui. 27, 1916. 



SOIL ACIDITY 357 

samples are brought to dryness over a steam bath and then 
taken up with about 100 cubic centimeters of water. The 
samples, after sliaking, are allowed to settle, and the super- 
natant liquid is treated with phenolphthalein. By the use 
of a number of samples with varying amounts of lime-water, 
the amount of the reagent necessary to neutralize the soil can 
be approximately determined. 

The objections that can be urged against the Veitch method 
may serve to indicate the difficulties that are in general en- 
countered in using most of the methods for determining the 
lime requirement of soils. The method is, in the first place, 
very artificial, there being no assurance that the amount of 
calcium absorbed is the same as that necessary to neutralize 
the soil under field conditions. In the second place, it is 
subject to considerable error. Even with the most careful 
manipulation, the method is hardly accurate within 300 
pounds of calcium oxide to the acre. 

If the results from such a method are to be applied directly 
to practical liming it must be assumed that the amount of lime 
necessary to neutralize an acid soil is the same as that capable 
of alleviating the acidity for a particular crop. In light 
of the variable influences of acidity on plants, this is an un- 
scientific assumption to say the least. Acidity itself is too 
intangible a condition. Moreover, it is in many cases not only 
inadvisable but also unprofitable to satisfy the full lime re- 
quirement of a soil. Some crops are unharmed or may even 
be benefited by moderate acidity. The selection of a lawn 
grass, for example, which is tolerant to acidity may allow 
the suppression of certain troublesome weeds that would 
spring up if the soil was limed. 

Since the results from lime-requirement methods must be 
so radically modified to suit field conditions, they seem but 
little better in a practical way than qualitative tests, which 
distinguish only in a general manner between different de- 
grees of acidity. The rapidity and simplicity of qualitative 



358 NATURE AND PROPERTIES OF SOILS 

tests give them an advantage over the somewhat questionable 
lime-requirement determinations. As the amount of lime 
applied is at best only an estimate, a simple test, rationally 
correlated with the many other factors that must be consid- 
ered, may prove as satisfactory as a more complicated pro- 
cedure. 

193. Qualitative tests for acidity — ^litmus paper. — Per- 
haps the oldest test for acidity is the use of litmus paper.^ 
This may be used alone or in connection with some sensitiz- 
ing agent. Potassium nitrate, a neutral salt, is often utilized 
in this capacity. As has already been explained (par. 141), 
the addition of such a salt, especially to a soil lacking in ac- 
tive bases, results in a marked selective absorption and the 
development of a hydrogen ion concentration. In using litmus 
paper and potassium nitrate it is assumed that the selective 
absorption and basic exchange is an approximate measure of 
the so-called soil acidity. 

The procedure is as follows: A small amount of the soil 
to be tested is placed in a small dish or other container and 
moistened with a neutral potassium nitrate solution. A thick 
batter is produced by mixing. The soil is then smoothed 
down and one end of a strip of neutral litmus paper is care- 
fully applied. The reddening of the paper is an indication 
of acidity, while the rate of the reaction is a rough measure 
of the degree. The portion of the paper not in contact with 
the soil may be used for comparison when the change is slight. 
The unused end may even be moistened with distilled water 
to make the comparison more accurate. 

194. The zinc-sulfide test. — Another qualitative test 
based on the same general principles has more recently been 

^ Barlow, J. T., Soil Acidity and the Litmus Paper Method for Its 
Detection; Jour. Amer. Soc. Agron., Vol. 8, No. 1, pp. 23-30, 1916. 

Karraker, P. E., The Value of Blue Litmus Paper from Different 
Sources as a Test for Soil Acidity; Jour. Amer. Soc. Agron., Vol. 10, 
No. 4, pp. 180-182, 1918. 



SOIL ACIDITY 359 

developed. This is the zinc-sulfide method.^ The soil sample, 
usually 10 grams, is placed in an Erlenmeyer flask and treated 
with an excess of neutral calcium chloride and zinc sulfide. 
About 75 cubic centimeters of water are added. The mixture 
is boiled for one minute to control frothing and to develop 
uniform ebullition. A strip of moistened lead acetate paper 
is now laid over the mouth of the flask and allowed to remain 
there exactly three minutes, the boiling being continued at 
a uniform rate. The reactions involved in the test are as fol- 
lows: 

Soil -f- xCaCL (neutral) ±5 Ca, Soil + xHCl 

2HC1 + ZnS = ZnCL + H,S 

H2S (Expelled by boiling) -f PMCHgO,). r= PbS 

(black) + 2C2H,0. 

The selective absorption and basic exchange of the soil de- 
velops actual acidity, which produces hydrogen sulfide from 
the zinc sulfide. The gas is driven off against the lead acetate 
paper, producing a black color. The principle involved is the 
same as that alreadj^ explained for the litmus test, a different 
means being employed for measuring the actual acidity de- 
veloped. 

195. Comparison and criticism of qualitative tests. — A 
comparison and criticism of these two methods will amply 
show the advantages and disadvantages of qualitative tests ^ 

^ Truog, E., Netv Method for the Determination of Soil Acidity ; 
Science, N. S., Vol. 40, pp. 246-248, 1914. 

Truog, E., Testing Soils for Acidity; Wis. Agr. Exp. Sta., Bui. 312, 
1920. 

' There are a number of other qualitative tests for acidity, of which 
the following may be mentioned: 

Ammonia test.- — In this test the soil is placed in a bottle and treated 
with a strong solution of ammonia. After shaking, the soil is allowed 
to settle, the depth of the color developing in the supernatant liquid 
being considered as indicating the degree of acidity. This color depends 
on the amount and character of the soil organic matter rather than on the 
acidity. 

Acid test for carbonates. — In this test a sample of the soil is treated 
with a few drops of dilute hydrochloric acid. Effervescence indicates the 



360 NATURE AND PROPERTIES OF SOILS 

in general. The litmus paper test is simple and rapid. It 
can be used with equal facility in the laboratory and field. 
While its readings may not correlate very definitely with the 
actual amount of lime that should be applied, it gives a basis 
for an estimate that in practice should include a number of 
factors besides so-called soil acidity. One objection to the 
method lies in the difficulty of obtaining sensitive litmus paper. 
Again the intensity of the color change is not great and in the 
hands of an inexperienced person may seem insignificant. In 
spite of its limitations, it is one of the best practical qualita- 
tive tests for soil acidity now available. 

The zinc-sulfide test is much more striking than the litmus 
test and thus is more easily interpreted. On account of the 
marked change of color there is always a temptation to read 
into this test a quantitative value which it does not possess 
to any greater degree than does the litmus paper method. 

The zinc sulfide test is not as rapid as the litmus test, nor is 
it a satisfactory field method. Moreover, it is more complex 
and requires a much more extensive technique. Again it does 
not distinguish between a neutral and an alkaline soil. Lit- 
mus paper, on the other hand, indicates alkalinity and acidity 
with equal facility. The zinc-sulfide test is not a method 
suited for those inexperienced in laboratory procedure. The 
deductions from the two tests, however, should be approxi- 
mately the same. 

196. Resume. — Soil acidity is a more or less unfavorable 
biological condition, which develops in soils due to the lack or 

presence of sufficient favorable bases in the carbonate or bicarbonate 
forms. A soil, however, may be alkaline and yet fail to effervesce. 

Potassium sulfo-cyanate test. — A new test has recently been proposed 
in which a sample of soil held in a test-tube is treated with an alcoholic 
solution of potassium sulfo-eyanate (KSCN). If the supernatant liquid 
turns red, soluble iron is present, the degree of color indicating the 
amount. It is assumed that the soluble iron is a comparative measure 
of the active aluminum in the soil and that aluminum is the toxic 
constituent. 

Comber, N. M., A Qualitative Test for Sour Soils; Jour. Agr. Sci., 
Vol. 10, part 4, pp. 420-424, 1920. 



SOIL ACIDITY 361 

inactivity of certain bases, especially those which tend to- 
wards soil alkalinity. These necessary bases may be rendered 
inactive by absorption phenomena or may be actually lost 
through leaching and cropping. The specific and usually de- 
leterious influence of so-called soil acidity may be due to an 
excessive hydrogen ion concentration or to toxic bases such 
as aluminum, iron, and manganese, which become active when 
ionic calcium and similar bases are lacking, thus encouraging 
a hydrogen ion accumulation. It is not improbable that in 
some cases the detrimental influence may be improper nutri- 
tion, either due to a lack of calcium as a nutrient or as a syner- 
gistic agent necessary for the absorption of other nutrients 
by plants. These detrimental conditions are alleviated in 
practice by the application of some form of lime. 

A number of different methods has been devised to ascer- 
tain quantitatively the lime requirements of soils. They are 
all more or less inaccurate. Moreover, the lime requirement 
of a soil and the lime necessary for best plant growth on that 
soil are not of necessity the same. Plants respond very differ- 
ently to the diverse conditions that may develop in the various 
acid soils and it is seldom necessary or practicable entirely to 
neutralize a very acid soil in order to correct its deleterious 
condition. While lime-requirement methods are valuable in 
research, qualitative tests are sufficient in practice. The 
amount of lime that should be applied is determined not only 
by the degree and nature of the acidity but also by the char- 
acter of the crops, the length of rotation, the system of fer- 
tilization, and similar factors. At best the amount of lime 
that should be applied to the acre is but an estimate based 
on many conditions, of which acidity is one. A qualitative 
test seems as satisfactory a basis for such an estimate as a 
more carefully controlled quantitative determination. 



CHAPTER XIX 
LIMING THE SOIL"^ 

While soil acidity is a condition but imperfectly under- 
stood, most investigators are agreed that it is due to a lack or 
inactivity of certain bases, especially those that tend to reduce 
the hydrogen ion concentration of the soil solution and to 
give the soil an alkaline reaction. The correction of acidity 
obviously lies in the addition of compounds which carry the 
necessary bases in such forms that the acidity may be partially 
or wholly alleviated. 

The base most commonly used to correct acidity is calcium, 
although magnesium is often applied, especially in connec- 

' The following publications may be of interest : 

Hopkins, C. G., Ground Limestone for Acid Soils; 111. Agr. Exp. Sta., 
Cire. 110, 1907. 

Ellett, W. B., Lime for Virginia Farms; Va. Agr. Exp. Sta., Bui. 187, 
1910. 

Brown, P. E., Bacteriological Studies of Field Soils: The Effects of 
Lime; la. Agr. Exp. Sta., Ees. Bui. 5, 1912. 

Whitson, A. E., and Weir, W. W., Soil Acidity and Liming; Wis. Agr. 
Exp. Sta., Bui. 230, 1913. 

Frear, W., Sour Soils and Liming; Penn. Dept. Agr., Bui. 261, 
1915. 

Miller, M. F., and Krusekopf, H. H., Agricultural Lime; Mo. ^r. 
Exp. Sta., Bui. 146, 1917. 

Mooers, C. A., Ground Limestone and Prosperity ; Tenn. Agr. Exp. 
Sta., Bui. 119, 1917. 

Shorey, E. C., The Principles of the Liming of Soils; U. S. Dept. Agr., 
Farmers' Bui. 921, 1918. 

McCool, M. M., and Millar, C. E., Some General Information on Lime 
and Itc Uses and Functions in Soils; Mich. Agr. Exp. Sta., Special Bui. 
91, 1918. 

Agee, Alva., The Bight Use of Lime in Soil Improvement ; New York, 
1919. 

Hudelson, R. R., Keeping Soils Productive ; Mo. Agr. Exp. Sta., Circ. 
102, 1921. 

362 



LIMING THE SOIL 363 

tion with calcium. Calcium is employed because it is not only 
effective with all types of acidity but because it is compara- 
tively cheap and plentiful. Potassium in active form is too 
expensive, sodium is likely to generate harmful compounds 
in the soil, while magnesium in large amounts is sometimes 
harmful. Calcium compounds may be applied in excess and 
yet no harmful effects on plant growth are ordinarily likely 
to result.^ 

197. Forms of lime. — The term lime correctly used re- 
fers only to calcium oxide (CaO). In a popular and agri- 
cultural sense the scope of the word has been broadened to 
include all of the commercial compounds of calcium and mag- 
nesium commonly applied to the soil to correct the so-called 
acidity. The term in its agricultural sense refers to the fol- 
lowing compounds either alone or in mixture : calcium oxide 
(CaO), magnesium oxide (MgO), calcium hydroxide (Ca- 
(OH),), magnesium hydroxide (I\Ig(0H)2), calcium car- 
bonate (CaCOg), and magnesium carbonate (MgCO^). Such 
compounds as gypsum (CaS04.2H20), mono-calcium phos- 
phate (CaH4(P04)2), and calcium silicate (Ca2Si04), insofar 
as they are carriers of calcium, also might be spoken of as lime. 

As might be expected, liming materials do not appear on the 
market as single compounds of magnesium or calcium, nor 
are they by any means pure. The better grades of the oxides 
and hj^droxides are generally used in the trades, the more im- 
pure materials having an outlet as agricultural lime. The car- 
bonated forms of lime have a number of different sources and 
vary to a marked degree in purity. Lime, in whatever form 
it may appear on the market, almost always carries magnesium 
as well as calcium, the latter usually predominating. 

Three general groups of lime, as it is commercially handled, 



^ Floyd, B. F., Some Cases of Injury to Citrus Trees Apparently 
Induced by Ground Limestone ; Fla. Agr. Exp. Sta., Bui. 137, 1917. 

Wyatt, F. A., Influence of Calcium a)id Magnesium Compounds on 
Plant Growth; Jour. Agr. Ees., Vol. VI, No. 16, pp. 589-619, 1916. 



364 NATURE AND PROPERTIES OF SOILS 

may be recognized: (1) burned lime/ (2) water-slaked or 
simply slaked lime,^ and (3) carbonated lime.^ 

The devices for producing burned lime are various, rang- 
ing from the farmer's lime heap to the immense cylindrical 
kilns of commerce. In any case the general result is the same. 
The limestone with which the kiln is charged is decomposed by 
the heat, carbon dioxide and other gases are discharged, and 
calcium and magnesium oxides are left behind.* The purity of 
burned lime, as it is sold for agricultural purposes, is quite 
variable, ranging from 60 to 98 per cent, of calcium and mag- 
nesium oxides. As high as 40 per cent, of burned lime may 
be magnesium oxide, if the original stone was dolomitic. The 
impurities of burned lime consist of the original impurities 
of the limestone, such as chert, clay, iron compounds, and the 
like, as well as unburned fragments of the stone. These ma- 
terials are often partially screened out before the product ap- 
pears on the market. 

Slaked lime is produced by adding water to the burned 
product, a hydroxide resulting from the direct union of the 
oxides of calcium and magnesium with water. ^ Often some 
of the calcium and magnesium oxides remain unslaked. Four 
lime compounds may, therefore, appear in freshly slaked lime, 
besides the original impurities of the burned materials. Com- 

* Often spoken of as burnt lime, oxide of lime and quick lime. It 
may be purchased either in the lump form or in a finely ground condi- 
tion. It is highly caustic and reacts readily with water. 

^ Incorrectly designated in trade as hydrated lime or lime hydrate. 
It is strongly alkaline and quite caustic but not to the degree exhibited 
by calcium and magnesium oxides. Calcium hydroxide and magnesium 
hydroxide are soluble in cold water to the extent of about 17 parts and 
.09 parts in 10,000, respectively. 

^ The carbonated forms of lime are often incorrectly spoken of as 
lime carbonate and carbonate of lime. Calcium and magnesium carbo- 
nates are soluble in pure cold water to the extent of only about .13 and 
1.06 parts in 10,000, respectively. The reaction to litmus is slightly 

"CaCO, -I- Heat = CaO + CO^. 

MgC03 + Heat = MgO + COj. 
»CaO-|-H20=Ca(OH)j. 

MgO -1- H,0 = Mg(OH),. 



LIMING THE SOIL 365 

mercial slaked lime ranges in composition from 60 to 75 per 
cent, of lime expressed as calcium plus magnesium oxides. 
Both the burned and slaked forms of lime tend to absorb car- 
bon dioxide from the air, producing calcium and magnesium 
carbonate. This is called air-slaking.^ 

A number of lime compounds are sold under the head of 
carbonated lime. Of these pulverized or ground limestone is 
the most common. There is also bog lime or marl, oyster 
shells and artificial carbonates. The latter are by-products 
from certain industries. All of these are quite variable in 
their content of calcium and magnesium carbonates. Pul- 
verized limestone may vary in purity from 75 to 98 per cent., 
90 per cent, being a fair average. Highly magnesian stone is 
generally avoided, although stone carrying from 15 to 20 per 
cent, of magnesium carbonate is often used. The magnesium 
carbonate, however, usually makes up less than 5 per cent, of 
the lime present. 

The figures - quoted in table LXXI (see page 366) show the 
average composition of liming materials offered for sale in 
Pennsylvania from 1916 to 1920 inclusive. 

198. Determining the need for lime. — The lack of lime 
in the soils of humid regions is so universal that liming will 
generally increase crop growth. For example, 72 per cent, of 
the soils of Pennsylvania ^ are sour, while 75 per cent, of the 
cultivated lands of Indiana * show acidity by the ordinary 
tests. While it is safe to assume that the productivity of 
three-fourths of the soils in the eastern part of the United 
States would be raised by liming, it is a question in many cases 
whether such treatment would pay. 

^ CaCOH), + CO2 = CaC03 + HA 
Mg(OH), + 00^ = MgCO, + HA 
^ Kellogg, J. W., Lime Beport ; Penn. Dept. Agr., Vol. 4, No. 2, Feb. 
1921. 

'White, J. W., Lime Bequirements of Pennsylvania Soils; Penn. Agr. 
Exp. Sta., Bui. 164, 1920. 

* Wiancko, A. T., Conner, S. D., and Jones, S. C, The Value of Lime on 
Indiana Soils; Ind. Agr. Exp. Sta., Bui. 213, 1918. 



366 NATURE AND PROPERTIES OF SOILS 
Table LXXI 




The first point to be determined in deciding whether or 
not lime should be applied is in regard to the acidity and its 
degree. The litmus or zinc sulfide test will supply this in- 
formation, although a quantitative determination may be 
made.^ The general degree of acidity, unless it is very high, 
is not sufficient, however, in deciding whether it would be 
wise to lime the soil. The nature of the crops is a .factor, 
as well as the type of the rotation, the fertilizer to be used, 
and to what extent farm manure and green-crops are utilized. 
Often special considerations are involved, such as scab on 
potatoes, which is encouraged by liming. All of the factors 
mentioned, as well as the experiences of the community with 
lime, should be considered in deciding whether liming would 
pay. If the increased crops that will probably result from 
an application of lime will not pay a good interest on the 
investment, then liming is not to be advised. An application 
sufficient to make possible the production of good crops of 
clover or alfalfa is probably all that can be used profitably. 

* The tests are discussed in Chapter XVIII. 



LIMING THE SOIL 367 

199. Form of lime to apply. — The experimental data 
regarding the relative effectiveness of the different forms of 
lime are not only meagre but also somewhat contradictory. 
In practice it is best to assume that the effectiveness of the 
lime depends on the amount of magnesium and calcium car- 
ried and is influenced to a much less degree by the particular 
combinations in which these bases may occur. For example, 
one and a half tons of medium to finely ground limestone 
carrying 50 per cent, of calcium oxide should be as effective 
as one ton of burned lime analyzing 75 per cent, calcium oxide. 
While there is a difference in the rapidity with which the 
various forms react, there seems to be but little difference be- 
tween them over the period of a rotation when they are ap- 
plied in chemical equivalent amounts. 

Accepting this relationship as a practical working basis, 
four factors must be considered in deciding what form of 
agricultural lime to apply. These factors are as follows: 
(1) chemical equivalents, determined by chemical combina- 
tion and purity; (2) cost a ton, freight on board; (3) freight; 
and (4) cost of haul and application to the land. 

It is evident that, if the various forms of lime are equally 
effective in chemical equivalent quantities, once these amounts 
are determined the question becomes a problem in arithmetic.^ 
The importance of the factors above listed can best be shown 
by working out an actual ease.^ 

^CaO X 1.32=:Ca(OfH)3 MgO X 1.44 = Mg(OH)3 

CaO X 1.78 = CaCOs MgO X 2.09 — MgCOg 

Ca(0H)2 X .76 = CaO Mg(0H)2 x .69 = MgO 

Ca(0H)2 X 1.3.5 = CaCO, MgCOH)^ x 1.44 = MgC03 
CaCOj X .56 = CaO MgCO, X .48 = MgO 

CaCOa X .74 = Ca(OH), MgCO, X .69 = Mg(OH), 

CaO X .70 = MgO MgO X 1.39 = CaO 

* Calcium oxide and calcium hydroxide have an advantage over ground 
limestone in percentages of calcium carried and possibly in initial ac- 
tivity. They are, however, more disagreeable to handle and do not 
mix M'ith the soil so well since they tend to lump on becoming moist. 
Partially or wholly carbonated lumps are often found in the soil years 
after the caustic lime has been applied. 



368 NATURE AND PROPERTIES OF SOILS 

Suppose that slaked lime carrying 70 per cent, of calcium 
oxide (CaO) sells in carload lots at $8.00 a ton and that pul- 
verized limestone of a fair degree of fineness costs in bulk 
$4.50 and analyzes 50 per cent, of calcium oxide. Assume the 
freight as $3.00 a ton and the cost of hauling to the farm and 
applying to the land as $1.00 more. 

The application of 1 ton of the agricultural slaked lime 
would cost $8.00 + $3.00 + $1.00 := $12.00. It would be 
necessary to apply 1.4 tons of the limestone to every ton of 
slaked lime. This would amount to $6.30 + $4.20 + $1.40 
= $11.90. The difference in this case is very slight be- 
tween the two forms. Lessening the freight or shortening 
the haul would give the advantage to the limestone, while in- 
creasing these would favor the use of slaked lime. 

It is obvious from such calculations that a flat recommenda- 
tion cannot be made in a county or community regarding the 
lime to use. Each individual case should be calculated, con- 
sidering the cost items already mentioned. 

200. Amount of lime to apply. — The possibility of an 
application of lime paying and the form to purchase can usu- 
ally be determined with considerable assurance. Such is not 
the case, unfortunately, regarding the amount of a given kind 
of lime to apply to the acre. So many factors, of which soil 
reaction is only one, are active in determining crop growth 
that acre applications are at best estimates and often admit- 
tedly guesses. Not only the degi-ee of acidity but the texture 
and the structure of the soil, the crops grown in rotation, the 
length of the rotation, the fertilizers used, the amount of farm 
manure added in a given period, and similar conditions must 
be considered. In ordinary practice, it is seldom economical 
to apply much more than a ton of limestone or its equivalent 
to the acre, unless the soil is very acid and the promise for 
increased crop yield exceptionally good. In many cases, it 
seems unnecessary entirely to correct the acidity of a soil in 
order to promote normal crop growth. The following figures, 



LIMING THE SOIL 369 

while merely tentative, serve in a general way as guides in 
practical liming operations for a four- or five-year rotation 
with average soils. The general degree of acidity may be 
estimated from a qualitative test. 

Table LXXXII 

suggested amounts of average pulverized limestone that 

should be applied to the acre under 

various conditions.^ 



Acidity 


Limestone — Pounds to the Acre 




Sandy Loam 


Clay Loam 


Moderate 


1200^1500 
1800I-2500 


1800-2500 


Strong 


2500-3000 



201. Changes of lime in the soil. — When calcium oxide or 
calcium hydroxide are added to the soil, they undergo a very 
rapid transformation, especially if the soil is moist. The 
oxide takes up water and becomes the hydroxide, while the 
latter almost as quickly changes to the carbonate. The reac- 
tions are as follows: 

CaO + H20 = Ca(OH)2 
Ca(OH), + CO2 = CaCOg + H2O 

It is generally supposed that when once the carbonate is 
formed in the soil or added as pulverized limestone, it is more 

* The equivalent amounts of burned or slaked lime may readily be 
calculated from the chemical equivalents already quoted. Calculate for 
example the amount of slaked lime, carrying 65 per cent, of CaO and 
5 per cent, of MgO, necessary to equal an application of 2000 pounds of 
adequately pulverized limestone containing 48 per cent, of CaO and 2 
per cent, of MgO. The 5 per cent, of MgO in the slaked lime and the 
2 per cent, of MgO in the limestone are equivalent in neutralizing capacity 
to 6.9 and 2.8 per cent, of CaO, respectively. The slaked lime and the 
limestone, therefore, carry the equivalent of 71.9 and 50.8 per cent, of 

9QQQ V 508 

CaO, respectively. ~ — ^—^ = 1413 pounds, the amount of slaked 

lime necessary to equal 2000 pounds of the limestone. 



370 



NATURE AND PROPERTIES OF SOILS 



or less stable, except for slow solubility. In most cases, how- 
ever, the carbonate, especially magnesium carbonate, is rap- 
idly decomposed and carbon dioxide is given off, the bases 
presumably entering the unsaturated aluminum silicates 
which are likely to be present in acid soils.^ 

The actual loss of lime in drainage water occurs through 
the influence of carbon dioxide which changes the insoluble 
carbonate to the soluble bicarbonate. The bicarbonate is 
washed out as such or ionizes, the calcium and the magnesium 
being lost in the ionic state. The presence of nitrates in the 
soil, either from biological activity or from fertilizers, also 
greatly facilitates the loss of lime from the soil in drainage. 
Such influence is to be especially expected during the summer 
and fall. In spite of the direct effect of carbon dioxide and 
nitrates on the loss of lime, the controlling factor seems to be 
the amount of water passing through the soil rather than its 
concentration. The following unpublished data from the 
Cornell University lysimeters show the losses of lime that may 
be expected under different conditions.^ These figures are 
averages of ten years' work with Dunkirk silty clay loam. 

Table LXXXIII 

average annual loss of nitrogen and lime by leaching, 
cornell lysimeters. average of 10 years. 



Condition 



Bare soil 
Rotation . 
Grass. . . 



Pounds to the Acre Per Year 



Nitrogen 



69.0 
7.3 
2.5 



LIME EX- 
PRESSED AS 

CaO 



557.0 
345.9 
363.8 



LIME EX- 
PRESSED AS 

CaCO, 



993.6 
617.1 
648.9 



^ Maclntire, et al., The Non-existence of Magnesium Carbonate in 
Humid Soils; Tenn. Agr. Exp. Sta., Bui. 107, 1914. 

'Complete data on these lysimeters will be found in par. 163. 



LIMING THE SOIL 371 

202. Effect of lime on the soil. — In heavy soils there is 
always a tendency for the fine particles to become too closely 
associated. Such a condition interferes with air and water 
movement. The ^-anular structure that should prevail is 
somewhat encouraged by the addition of lime, especially the 
caustic forms. In practice, however, the amounts of lime ap- 
plied are generally too small to have much importance in this 
respect. 

Chemically, lime brings about many complex changes in 
the soil. Basic exchange is forced and certain mineral nu- 
trients tend to become more available. The hydrogen ion 
concentration is lowered and deleterious bases, such as alumi- 
num and manganese, are forced back into less active combi- 
nations. Oxidation processes seem also to be stimulated, thus 
favoring tlie elimination of organic toxins, which often de- 
velop when improper decay takes place. The charge that 
quicklime in normal amounts produces a rapid and detri- 
mental oxidation of the soil organic matter is probably an 
over-statement.^ AVliile lime of all kinds promotes the oxida- 
tion of organic matter, calcium oxide, when added in rational 
amounts, is probably no more active over the term of the rota- 
tion than calcium carbonate. 

Most of the favorable soil organisms and some of the un- 
favorable ones, such as those that produce potato-scab, are 
benefited by judicious liming. The bacteria that fix nitrogen 
from the air, either alone or in the nodules of some legumes, 
are especially stimulated by the application of lime. The 
change of ammoniacal nitrogen to the nitrate form, which is a 
biological phenomenon, requires active basic material. Other- 
wise this necessary transformation will not proceed. The 
decomposition of both carbohydrate compounds (fermenta- 
tion) and of nitrogenous materials (putrefaction) depends on 
lime, that the decay products may be favorable. 

^Maclntire, W. H., The Carhonation of Burned Lime in Soils; Soil 
Sci., Vol. VII, No. 5, pp. 325-446, May, 1919. 



372 NATURE AND PROPERTIES OF SOILS 

Of the general and specific influences of lime just men- 
tioned the correction of acidity is the one commonly ascribed 
to it in the popular mind. The mere correction of the soil 
reaction, however, is probably no more important than a 
number of other direct and indirect influences of lime. It is 
evident that the benefits that may result from liming a soil 
will accrue from a combination of influences rather than from 
one effect alone. 

203. Crop response to liming. — Much experimental work 
has been done in various parts of the world in determining 
the relative response of different crops to liming and the rea- 
son for certain well-known differences. As might be expected, 
the results, while in close agreement as to some crops, show 
striking disagreements as to others. This is to be expected, 
since the varying conditions of the experiments would have a 
marked influence on the response of the plants under con- 
sideration. 

Of legume crops, alfalfa and red and white clovers respond 
most markedly to lime. The response of soybeans, garden 
peas and field peas, while less, is still quite noticeable. Alsike 
clover is more tolerant to acidity than red clover and, as the 
soil of a region declines in active bases, it is common to find 
it gradually replacing the latter. Japanese clover, cowpeas, 
vetch, and field beans do not seem to be greatly benefited by 
lime. 

Of the non-legumes that are favorably influenced by lime, 
blue-grass, maize, timothy, oats, barley, wheat, and sorghum 
may be mentioned. Rye is less benefited by liming than is 
barley. Red-top, cotton, strawberries, and potatoes do not 
seem to be particularly stimulated by liming. Certain plants, 
such as blueberries, watermelons, and rhododendron are ac- 
tually injured by the use of lime. 

There are a number of reasons why plants may be benefited 
by lime, these reasons being numerous and complex enough 
to account for the differences in response among common 



LIMING THE SOIL 373 

crops. The possible influences of lime on plants may be listed 
as follows: (1) direct nutritive action; (2) synergistic rela- 
tionships either in the soil solution or in the cell-wall; (3) re- 
moval or neutralization of toxins of either an organic or inor- 
ganic nature; (4) effect on plant diseases; (5) liberation of 
mineral nutrients; and (6) encouragement of the biological 
preparation of nutrient materials. 

In some cases the calcium may function as a direct nutrient ; 
in others the intake of nutrients may be facilitated by the 
presence of calcium and magnesium ; while in still other cases 
the elimination or alleviation of a toxic condition may be the 
important result. It is easy to conceive that any two or all 
three of these relationships might be fulfilled simultaneously 
by lime. The stimulating influence of lime might also make 
the plant a more active agent and thus encourage it to aid 
to a greater extent in the preparation of its own nutrients. 
Certain diseases may be retarded or even entirely suppressed 
by lime, as is the "finger-and-toe" disease of the Cruciferae. 

The liberation of mineral nutrients, such as potash and 
phosphoric acid, by the addition of lime, is somewhat uncer- 
tain although it evidently does occur in many cases.^ The 
process is probably a more or less complicated physical or 
chemical change. The stimulation to plants by such an ac- 
tion is difficult to establish, since so many disturbing factors 
are active in obscuring the results. Lime is undoubtedly very 
important in the use of acid phosphate, the active compound 
of which is mono-calcium phosphate (CaH4(P04)o). In the 
presence of active calcium, the reversion compound is 
(Ca3(P04)2),^ rather than the very insoluble iron and alumi- 
num phosphates (FePO^ and AIPO4). 

The formation of nitrates proceeds rather slowly in most 

^Plummer, J. K., The Effects of Liming on the Availability of Soil 
Potassium, Phosphorus and Sulfur; Jour, Amer. Soc. Agron., Vol. 13, 
No. 4, pp. 162-171, 1921. 

^CaH,(PO0, + 2CaH,(C03)2 = Ca3(PO,)2 + 4H,0 -|- 4C0, 



374 NATURE AND PROPERTIES OF SOILS 

acid soils, since there is but little active basic material to 
stimulate the nitrifying organisms directly or to neutralize 
the nitrous acid that is formed/ The addition of lime is the 
most economical method of supplying this base. This response 
of the nitrifying bacteria to lime is a matter of great moment 
to crops that need large amounts of nitrate nitrogen and may 
account in some cases for the early response of certain crops 
to liming. The tolerance of some plants to acid soils might be 
accounted for on the supposition that they need but small 
amounts of nitrogen or are able to absorb their nitrogen in 
forms other than the nitrate. 

204. Method and time of applying the lime. — Although 
lime is lost rapidly from most soils, appearing in the drain- 
age water in large amounts, it does not seem to correct to any 
great extent the acidity of the soil layers through which it is 
carried.^ Lime applied at the soil surface will tend to disap- 
pear, but will have little effect on the soil below. The action 
of lime seems to be a contact phenomenon and the more thor- 
oughly it is mixed with the soil, the greater will be the num- 
ber of active focii and the more rapid and effective will be the 
results of the treatment. 

Lime Is best applied to plowed land and worked into the soil 
as the seed-bed is prepared. It should be thoroughly mixed 
with the surface three to five inches of soil. Top-dressing of 
lime is seldom recommended except on permanent meadows 
and pastures. The time of year at which lime is applied is 
immaterial, the system of farming, the type of rotation, and 
such considerations being the deciding factors. The soil 
should not be too moist when the application is made, as the 

» 2NH8 + 3O2 = 2HNO2 + 2H,0. 
2HNO2 -f CaCOa = Ca(N0,)2 + H,0 + CO,. 
Ca(N0,)2 + O, = Ca(N03).. 
^Wilson, B. D., The Translocation of Calcium in a Soil; Cornell Agr. 
Ex^. Sta., Memoir 17, 1918. 

Stewart, E., and Wyatt, F. A., Limestone Action on Acid Soils; IlL 
Agr, Exp. Sta., Bui. 212, 1919. 



LIMING THE SOIL 375 

lime, especially the slaked and ground burned forms, tends to 
ball badly and thus thorough distribution is prevented. 

A lime distributer should be used, especially if the amount 
to be applied is at all large. A manure-spreader can be util- 
ized and even an end-gate seeder may be pressed into service. 
Small amounts of lime may be distributed by means of the 
fertilizer attachment on a grain drill. As with the applica- 
tion of any material, the evenness of distribution is as im- 
portant as the form and amount of lime used and should by no 
means be neglected. 

A discussion of the application of lime is never complete 
without some consideration being given to the place in the 
rotation at which the liming is best done. In a rotation of 
maize, oats, wheat, and two years of clover and timothy, the 
lime is often applied when the wheat is seeded in the fall. It 
can then be spread on the plowed ground and worked in as 
the seed-bed is prepared. Its effect is thus especially favor- 
able on the new seeding. Thorne ^ has shown, however, in 
certain Ohio experiments, that maize is affected more favor- 
ably than any of the crops above mentioned and as the money 
value of this increase is practically as much as that from the 
hay, he favors applying the lime to the maize. With pota- 
toes in the rotation, the lime should follow the potato crop, 
especially if scab is prevalent. In practice the place of lime 
in the rotation is usually determined by expediency, since the 
vital consideration is, after all, the application of lime regu- 
larly and in conjunction with a rational rotation of some kind. 

205. The calcium and magnesium ratio. — A physiological 
balance seems to be necessary in a nutrient solution in con- 
tact with a normally growing plant. This balance varies with 
the plant and with numerous other conditions. The reason 
for such antagonistic action between the ions of certain ele- 
ments is difficult to explain and many theories have been ad- 

^ Thome, C. E., The Maintenance of Fertility. Liming the Land; 
Ohio Agr. Exp. Sta., Bui. 279, 1914. 



376 NATURE AND PROPERTIES OF SOILS 

vanced. Loew/ in 1901, worked out the optimum ratio for 
a number of different plants growing in water culture. He 
found that both calcium and magnesium alone were toxic and 
it was only when the ratio of these ions fell within certain 
limits that the toxicity disappeared. This ratio varied be- 
tween 1 of CaO to 1 of MgO and 7 of CaO to 1 of MgO. 

The question was immediately raised as to the advisability 
of using limestone or even burned and slaked lime, the mag- 
nesium content of which approached in any degree the cal- 
cium present. Recent field and laboratory tests have shown, 
however, that magnesium salts may be applied in ordinary 
amounts alone or with calcium compounds with impunity.' 
The absorptive capacity of the soil seems to take care in a 
very effective way of any toxicity that might result from a 
soil solution physiologically unbalanced. 

206. The fineness of limestone. — The hardness of the 
stone, its purity, and its fineness are items of extreme im- 
portance to the manufacturer of pulverized lime. The softer 
the limestone, the easier the grinding and the finer the product 
with a given expenditure of power. The higher the percent- 
age of calcium and magnesium, the greater is the effectiveness 
of a given quantity. The farmer, other conditions being more 
or less equal, is especially interested in the fineness of the 
product. It is a well-known fact that the finer the division of 
any material, the more rapid the solution. This, however, 

^ Loew, O., The Physiological Bole of the Mineral Nutrients of Plants; 
U. S. Dept. Agr., Bur. Plant Ind., Bui. 1, p. 53, 1901. 

* Gile, P. L., and Ageton, C. IJ., The Significance of the Lime-Mag- 
nesia Ratio in Soil Analyses; Jour. Ind. and Eng. Chem., Vol. 5, pp. 
33-35, 1913. 

Thomas, W., and Frear, W., The Lime-Magnesia Patio in Soil Amend- 
ments; Jour. Ind. and Eng. Chem., Vol. 7, No. 12, pp. 1042-1044, 
Dec. 1915. 

Lipman, C. B., A Critique of the Hypothesis of the Lime-Magnesia 
Patio; Plant World, Vol. 19, No. 4, pp. 83-105, Apr. 1916. 

Wyatt, F. A., Influence of Calcium and Magnesium Compounds on 
Plant Groivth; Jour. Agr. Kes., Vol. VI, No. 16, pp. 589-619; 1916. 

Stewart, R., and Wyatt, F. A., Limestone Action on Acid Soils; 111. 
Agr. Exp. Sta., Bui. 212, 1919. 



LIMING THE SOIL 



377 



is not the only importance of fineness. Lime produces its in- 
fluence largely through contact, and the finer the lime is 
ground, the more thorough is the mixing with the soil and 
the greater the number of operating focii. 

White ^ presents the following significant data as a result 
of certain laboratory and greenhouse studies at State College, 
Pennsylvania. 

Table LXXXIV 

a comparison of various grades " of limestone when 
applied at the same rates. 



Conditions 



Solubility in carbonated w^ater 
Value in correcting acidity . . . . 

Formation of nitrates 

Plant growth 



100 Mesh 

AND 

Smaller 



100 
100 
100 
100 



60-80 


20-40 


Mesh 


Mesh 


57 


45 


57 


27 


94 


56 


69 


22 



8-12 
Mesh 

28 

18 

12 

5 



These figures show that the finer grades of limestone are 
much more rapidly effective. Further data by the same au- 

* White, J. W., The Value of Limestone of Different Degrees of Fine- 
ness; Penn. Agr. Exp. Sta., Bui. 149, 1917. Also, Thomas, W., and 
Frear, W., The Importance of Fineness of Sub-division to the Utility of 
Crushed Ldmestone as a Soil Amendment ; Jour. Ind. and Eng. Chem., 
Vol. 7, No. 12, pp. 1041-1042, 1915. 

Broughton, L. B., et al, Tests of the Availahility of Different Grades 
of Ground Limestone; Md. Agr. Exp. Sta., Bui. 193, 1916. 

Kopeloff, N., The Influence of Fineness of Division of Pulverized 
Limestone on Crop Yield as Well as the Chemical and Bacteriological 
Factors in Soil Fertility; Soil Sci., Vol. IV, No. 1, pp. 19-67, 1917. 

Frear, W., The Fineness of Lime and Limestone Application as Be- 
lated to Crop Production; Jour. Amer. Soc. Agron., Vol. 13, No. 4, 
pp. 171-174, 1921. 

''Lime is graded by sieves carrying a certain number of meshes to the 
linear inch. An 80-niesh sieve has 80 openings to the linear inch or 6400 
to the square inch. Screens rated as carrying the same number of meshes 
often do not give the same grade of material, due to a difference in the 
size of wire used. Material of 60 to 80 mesh refers to those sizes that 
will pass through a 60-mesh but will be held by an SO-mesh screen. 
A standardization of sieves and methods of expressing such analyses is 
much needed. 



378 



NATURE AND PROPERTIES OF SOILS 



thor indicate that while the coarser lime is less rapid in its 
action, it remains in the soil longer and its influence should 
be effective for a greater period of years. 

Table LXXXV 

decomposition of limestone during the three years 
after application. 





Percentage of Decomposition 


Mesh 


High Calcium 
Stone 


High Magnesium 
Stone 


100 mesh and smaller. . . 
60 to 80 mesh 


92.4 
81.5 
46.7 
14.9 


91.2 

72.2 


20 to 40 mesh 

8 to 12 mesh 


34.9 
5.9 



The conclusion is likely to be drawn that limestone should 
be ground as finely as possible. Such an assumption is at 
fault in several ways. In the first place, very fine lime is 
difficult to handle and unpleasant to distribute. Again, the 
cost of grinding increases very rapidly with the fineness, being 
entirely too expensive compared with the results attained. 
Moreover, finely ground material does not possess the lasting 
qualities of the coarser lime. Because of the cost of grinding 
the stone to a very fine condition and the rapidity with which 
such material disappears from the soil, a medium ground 
lime seems to be a more desirable commercial product. Such 
material has enough of the finer particles to give quick re- 
sults and yet enough of the coarser fragments to make it last 
over the period of the rotation. A pulverized limestone, all 
of which will pass a 10-mesh sieve, 70 per cent, of which 
will pass a 50-mesh sieve and 50 per cent, of which will pass 
a 100-mesh sieve, should give excellent results and yet be 
cheap enough to make its use worth while. 

The following figures show in an approximate way the 



LIMING THE SOIL ^79 

mechanical composition of limestone on sale in Pennsylvania 
for 1920^: 

Table LXXXVI 

mechanical composition of some limestone offered for 
sale in pennsylvania in 1920. 



Limestone 


Amount Passing Sieve, Mesh 




10 


50 


100 


1 


100 
100 
100 
100 
100 
100 


98 
99 
89 
70 
57 
44 


92 


2 


88 


3 


73 


4 


58 


5 


50 


6 


34 







207. Gypsum and other soil amendments. — Gypsum, in 
which form calcium sulfate (CaS04.2H20) is usually applied 
to soil, has been used for years and was popular long before 
commercial fertilizers were available to any extent. The use 
of gypsum was probably familiar to the Romans. It fre- 
quently goes by the name land plaster. It is widely distribu- 
ted in nature and easily ground. Its beneficial effect has been 
noted, particularly with clover and alfalfa, crops which re- 
spond especially to potash. Its popularity has waned in recent 
years, however, since its effectiveness on soils where it has 
long been used has apparently decreased. This possibly has 
been due in part to the acid residue that ultimately must re- 
sult from the use of such material and to the failure to lib- 
erate potassium — a property with wliich it has very gen- 
erally been credited and which, when applied to some soils, 
it may possess. The experimental work in this respect is 
somewhat conflicting, possibly due to the fact that the con- 

* Kellogg, J. W., Lime Eeport; Penn. Dept. Agr., Vol. 4, No. 2, 
1921. 



380 NATURE AND PROPERTIES OF SOILS 

ditions of contact between the soil and the gypsum were ab- 
normal. McMillar ^ found that the potash of certain Minne- 
sota soils treated with one per cent, of gypsum was appre- 
ciably influenced three months after the application. When 
gypsum has proven beneficial to crop growth, the effect may 
have been due to the nutrient influence of the sulfur it con- 
tains or to the potash liberated from its soil combinations. 
The use of gypsum as a soil amendment is now seldom recom- 
mended, especially if the other forms of lime are available. 

Sodium chloride has a marked effect on the productivity of 
some soils, especially when certain crops such as asparagus 
are grown. Wherein its effectiveness lies is not well under- 
stood. Increased fertility arising from the addition of sodium 
and chlorine, which are plant constituents, is probably not 
the reason of its influence, as these substances are usually 
available in soils far beyond any possible plant requirement. 
When common salt shows a beneficial influence, it is probably 
due to its tendency to liberate certain mineral nutrients such 
as potassium, calcium, and magnesium. Since it tends to 
leave an acid residue in the soil and since some form of lime 
will generally give better and more permanent results, the 
use of common salt is not recommended except in certain 
cases. 

The use of di-calcium silicate (Ca2Si04) in an experimental 
way as a liming material has recently received some attention. 
Cowles,^ in 1917, presented data from which he concluded that 

^ McMillar, P. E., Influence of Gypsum upon the Solubility of Potash 
in Soils; Jour. Agr. Ees., Vol. XIV, No. 1, pp. 61-66, 1918. 

Morse, F. W., and Curry, B. E., The Availability of Soil Potash in 
Clay and Clay Loam Soils; N. H. Agr. Exp. Sta., Bui. 142, 1909. 

Bradley, C. E., The Reaction of Lime and Gypsum on Some Oregon 
Soils; Jour. Ind. and Eng. Chem., Vol. 2, No. 12, pp. 529-530, 1910. 

Briggs, L. J., and Breazeale, J. F., Availability of Potash in Certain 
Orthoclase-bearing Soils as Affected by Lime or Gypsum; Jour. Agr. 
Res., Vol. VIII, No. 1, pp. 21-28, 1917. 

^Cowles, A. H., Calcium Silicates as Fertilizers. Metal. Chem. Eng., 
Vol. 17, pp. 664-665, 1917. 



LIMING THE SOIL 381 

this compound was of greater value than either ground lime- 
stone or slaked lime as an amendment. He also concluded 
that silicon was an essential element in plant nutrition. Hart- 
well and Pember/ in 1920, found di-calcium silicate approxi- 
mately equal to limestone insofar as the correction of acidity 
was concerned. Lettuce was used as an indicator. They 
found no indication that the silicon was of any value, but, as 
their experiments were with soil, this, of course, does not op- 
pose the idea that silicon is an essential element in the growth 
of plants. 

Hartwell and Pember concluded that the beneficial influ- 
ence of phosphorus and calcium compounds added to the soil 
might, in many cases, be due to the precipitation of active 
aluminum quite as much as to the supplying of nutrients or 
the correction of actual acidity. Such a conception of the 
influence of liming materials may ultimately mean an in- 
crease in the number and nature of the compounds that may 
be used as soil amendments. 

208. Importance of lime in soil improvement." — The in- 
fluence of successively liming a soil over a period of years 
may tend to raise or lower the fertility of the soil, according 
to the system of soil management that accompanies the appli- 
cations of the lime. The use of lime alone will undoubtedly 
increase crop yield for a time. Basic exchange will be en- 

* Hartwell, B. L., and Pember, F. K., The Effect of Dicalcium Silicate 
on an Acid Soil; Soil Sci., Vol. X, No. 1, pp. 57-60, July, 1920. 

^ A number of general references on the importance of lime were 
given at the beginning of the chapter. See also, 

Wiancko, A. T., et al., The Value of Lime on Indiana Soils; Ind. Agr. 
Exp. Sta., Bui. 213, 1918. 

Stewart, R., and Wyatt, F. A., Limestone Action on Acid Soils; 111. 
Agr. Exp. Sta., Bui. 212, 1919. 

Lipman, J. G., and Blair, A. W., The Lime Factor in Permanent 
Soil Improvement; Soil Sci., Vol. IX, No. 2, pp. 83-114, Feb. 1920. 

Hartwell, B. L., and Damon, S. C, Sta; Tears' Experience in Improving 
a Light Uiiproductive Soil; Jour. Amer. Soc. Agron., Vol. 13, No. 1, 
pp. 37-41, Jan. 1921. 



382 NATURE AND PROPERTIES OF SOILS 

couraged, soil bacteria will be stimulated, and more nutrients 
will become available for crop use. Such stimulation, how- 
ever, will soon wane, and if nothing is returned to the land, 
productivity must ultimately drop back to even a lower level 
than before the lime was applied. 

Lime is, to a great extent, a soil amendment and as it in- 
creases crop growth, the draft on the soil becomes larger. 
Greater effort is necessary, therefore, in order to maintain 
the fertility of the land when lime is used than when such ap- 
plications are not made. Farm manure, crop residues and 
green-manures should be utilized to the fullest extent and 
when these are insufficient to keep up the potash and phos- 
phoric acid of the soil, commercial fertilizing materials must 
be resorted to. Lime improperly used exhausts the soil, but 
when properly and rationally applied it becomes one of the 
important factors in the maintenanoe of a more or less con- 
tinuous productivity. 

It is interesting in this connection to consider certain fig- 
ures from the Ohio Experiment Station.^ Maize, oats, wheat 
and clover and timothy were grown in a five-year rotation 
on both limed and unlimed plats fertilized in various ways. 
The results of table LXXXVII (page 383) are averages for a 
period of twelve years. 

It is immediately evident that the effectiveness of the lime 
was increased by the use of both fertilizers and farm manure. 
Conversely, the returns from the fertilizers and the manure 
were markedly influenced by the lime. The lime increased 
the effectiveness of the acid phosphate 20 per cent. The in- 
creases with the acid phosphate plus potassium chloride and 
with the complete fertilizers were 22 and 10 per cent., re- 
spectively. Lime increased the returns of farm manure only 
4 per cent., indicating that manure itself may function as a 

^ Thome, C. E., The Maintenance of Soil Fertility. Liming the Land; 
Ohio Agr. Exp. Sta., Bui. 279, 1914. 



LIMING THE SOIL 



383 



Table LXXXVII 

relative rotation values of crop increases due to liming 
and fertilizing a standard rotation over a twelve- 
year period. ohio experiment station. the acid 
phosphate treatment is taken as 100 for 
the lime gain and also for the 
unlimed fertilizer gain. 



Fertilizers to the Dotation 


Gain 

FROM 

Lime 


Gain prom Fer- 
tilizers 




Unlimed 


Limed 


Acid phosphate 

Acid phosphate plus potassium 
chloride 


100 

114 

119 
113 


100 
142 

232 

287 


120 
173 


Acid phosphate, potassium 

chloride and sodium nitrate 

Manure, 16 tons 


255 
300 



soil amendment. These figures serve in a definite way to em- 
phasize the correlation between liming and the other factors 
that must be considered in soil improvement and fertility 
maintenance. 



CHAPTER XX 

SOIL ORGANISMS,' CARBON, SULFUR, AND 
MINERAL CYCLES 

A VAST number of organisms, both vegetable and animal, 
live in the upper layers of the soil and determine to a very 
large degree its dynamic character.^ By far the greater por- 
tion of these organisms belong to plant life, producing those 
changes, both organic and inorganic, which control, in large 
degree, the productivity of the soil. While most of the or- 
ganisms are so minute as to be seen, if visible at all, only by 
the aid of a microscope, a small proportion attain the size of 
the larger rodents. For convenience of discussion the life of 
the soil may be classified into macro-organisms and micro- 
organisms. 

209. Macro-organisms — animal forms. — Of the macro- 
organisms in the soil, the animal types are chiefly (1) rodents, 
(2) worms, and (3) insects; and the plant forms (1) the 
large fungi and algse, and (2) roots. 

The burrowing habits of rodents — of which the ground 
squirrel, the mole, the gopher, and the prairie dog are familiar 
examples — result in the pulverization of considerable quanti- 

^ General references : 

Lipman, J. G., Bacteria in Selation to Country Life; New York, 
1908. 

Conn, H. W,, Agricultural Bacteriology ; Philadelphia, 1918. 

Marshall, C. E., Microbiology ; Philadelphia, 1917. 

^ It has iaeen estimated that every acre of soil contains at least 2000 
pounds of living material exclusive of roots. If these organisms were 
confined to a surface foot of soil, weighing, when moist, 4,000,000 pounds 
to the acre foot, they would make up .05 per cent, by weight of the nor- 
mal field soil. 

384 



SOIL ORGANISMS 385 

ties of soil. While the effect is rather beneficial and is analo- 
gous to tillage, the activities of these animals are generally 
unfavorable to agricultural operations and such soil inhabi- 
tants have been more or less exterminated in arable land. 

The common earthworm is the most conspicuous example of 
the benefits that may accrue from the presence of animals. 
Darwin, as the result of careful measurements, states that the 
quantity of soil passed through these creatures may under 
favorable conditions in a humid climate, amount to ten tons 
of dry earth to the acre annually. The earthworm obtains its 
nourishment from the organic matter of the soil, but takes 
into its alimentary canal the inorganic matter as well, ex- 
pelling the latter in the form of casts after it has passed en- 
tirely through the body. The ejected material is to some ex- 
tent disintegrated, and is in a flocculated condition. The holes 
left in the soil serve to increase aeration and drainage. The 
activities of the worms bring about a notable transportation 
of lower soil to the surface, which aids still more in effecting 
aeration. Darwin's studies led him to state that from one- 
tenth to two-tenths of an inch of soil is yearly brought to the 
surface of land in which earthworms exist in numbers normal 
to fertile soil. 

Earthworms naturally seek a heavy compact soil, and it is 
in soil of this character that they are most needed because of 
the stirring and aeration that they accomplish. Sandy soil 
and that of arid regions, in which are found few or no earth- 
worms, are not usually in need of their activities. 

There is a less definite, and probably a less effective, action 
of a similar kind produced by insects. Ants, beetles, and the 
myriads of other burrowing insects and their larvae effect a 
considerable movement of soil particles, with a consequent 
aeration of the soil. At the same time they incorporate into 
the soil a considerable quantity of organic matter. 

210. Macro-organisms — plant forms. — The larger fungi 
are chiefly concerned in bringing about the first stages in the 



386 NATURE AND PROPERTIES OF SOILS 

decomposition of woody matter, which is disintegrated by the 
penetrating mycelia of the fungi. These break down the 
structure, and thus greatly facilitate the work of the decay 
bacteria. Action of this kind is largely confined to the forest 
and is not of great importance in cultivated soil. Another 
function of the large fungi is exercised in the intimate, and 
possibly symbiotic, relation of the fungal hyphse to the roots of 
many forest trees, in soil where nitrification proceeds very 
slowly, if at all, for nitrates are apparently not abundant in 
forests. 

Algse, except in special cases, do not exist in the soil to 
any large extent. Certain Colorado soils,^ however, seem to 
contain appreciable numbers of this form. While the pres- 
ence of both the larger fungi and the algas is interesting, their 
importance in soil fertility is probably rather slight. 

The roots of plants are important in the soil both by con- 
tributing organic matter and by leaving, on their decay, open- 
ings which render the soil more permeable to air and water. 
The dense mass of rootlets, with their minute hairs, that is left 
in the soil after every harvest, furnishes a well-distributed 
supply of organic matter, which is not confined to the furrow 
slice, as is artificially incorporated manure. The action of 
roots on the soil is not by any means entirely physical. Dur- 
ing the life of the plant the elimination of tissue and the 
presence of exudates make the rootlets rather important chem- 
ical agents.- The chemical and biological importance of de- 
caying organic matter has already been adequately empha- 
sized.^ 

211. Micro-organisms — protozoa. — The micro-organisms 
of the soil belong to the following groups: (1) protozoa, (2) 
fungi and algse, (3) actinomyces, and (4) bacteria, 

^ Bobbins, W. W., Algce in Some Colorado Soils; Colo. Agr. Exp. Sta., 
Bui. 184, 1912. 

^See paragraphs 156 and 157. 
* See paragraphs 64 and 132. 



SOIL ORGANISMS 387 

While nematodes, rotifers, and similar organisms are some- 
times found in soil, the protozoa are the only important micro- 
scopic animal group usually present. The importance of 
protozoa in soils was especially emphasized in 1909 by Russell 
and Hutchinson,^ who maintained that the protozoan flora so 
interfered with the ammonia-producing bacteria as materially 
to lower the productivity of the soil. Partial sterilization 
seemed to alleviate this condition, possibly by killing the 
harmful protozoa. The findings of Russell and Hutchinson 
have resulted in much research as to the importance of proto- 
zoa in a normal soil. 

While Waksman ^ found that the presence of protozoa was 
concomitant with low bacterial numbers, he does not consider 
all protozoa harmful to biological activities. Fellers and Alli- 
son,^ in an examination of New Jersey soils, found protozoa in 
every sample, the number of species ranging from two to 
twenty-eight. Soils rich in organic matter or containing large 
amounts of water carried the greater number. Besides the 
104 species of protozoa identified in New Jersey soils, ten 
genera of algffi and six of diatomes were isolated. Nematodes 
were common. The number of protozoa ranged from a very 
few to as high as 4500 to a gram of soil. When occurring in 
such numbers, these animals must be of considerable impor- 

' Russell, E. G., and Hutchinson, H. B., The Effect of Partial Sterili- 
zation of Soil on the Production of Plant Food; Jour. Agri. Sci., Vol. 
Ill, pp. 111-144, 1909. Also, TJie Effect of Partial Sterilization of 
Soil on the Production of Plant Food. II. The Limitation of Bac- 
terial Numbers on Soils and Its Consequences ; Jour. Agr. Sci., Vol. V, 
part 2, pp. 152-221, 1913. 

' Waksman, S. A., Protozoa as Affecting Bacterial Activities in the 
Soil; Soil Sci., Vol. II, No. 4, pp. 363-376, 1916. Also, Sherman, 
J, M., Studies on Soil Protozoa and Their Relation to the Bacteria; 
I. Jour. Bact., Vol. 1, No. 1, pp. 35-66, 1916. II. Jour, Bact., Vol. 1, 
No. 2, pp. 165-184, 1916. 

Kopeloff, N., and Coleman, D. A., A Beview of Investigations in 
Soil Protozoa and Soil Sterilization; Soil Sci., Vol. Ill, No. 3, pp. 
197-269, 1917. 

'Fellers, C. R., and Allison, F. E., The Protozoan Fauna of the 
Soil of New Jersey; Soil Sci., Vol. IX, No. 1, pp. 1-24, 1920. 



388 NATURE AND PROPERTIES OF SOILS 

tance in soils, although it is doubtful whether they are detri- 
mental except under special conditions.^ 

212. Micro-org-anisms — fungi and algae. — Of the higher 
fungi, molds are the only group that apparently attain any 
particular importance in soils, although yeasts have been found 
to occur and may in special cases exist in considerable num- 
bers. It is only recently, however, that fungi have received 
much attention, although their presence has been noted many 
times. Such common genera as Fusarium, Mucor, Aspergillas, 
and Pencillium are usually present in normal soils. In gen- 
eral, a large amount of organic matter is conducive to the 
activity of such fungi. Molds occur in soils in both the active 
and the spore stage and probably pass their various life cycles 
entirely in the soil. 

Waksman,^ in a detailed study of soil fungi, found that 
most of the organisms were capable of producing considerable 
ammonia from nitrogenous organic matter. A large propor- 
tion of the fungi isolated were also able to decompose cellulose 
rather rapidly. Different soils seemed to have a distinct and 
characteristic fungal flora. Over one hundred distinct species 
of fungi were isolated by Waksman belonging to thirty-one 
genera. Some pathogenic species, such as different Fusaria 
and Alternaria, were found. The numbers ranged from 80,- 
000 to a gram of soil under forest conditions to 14,000,000 
to a gram in a meadow soil. The numbers were usually larger 

^ Koch, G. P., Studies on the Activity of Soil Protozoa; Soil Sci., 
Vol. II, No. 2, pp. 163-181, 1916. 

'Waksman, S. A., Soil Fimgi and Their Activities; Soil Sci., Vol. 
II, No. 2, pp. 103-155, 1916. Also, 

McLean, H. C, and Wilson, G. W., Ammonification Studies with Soil 
Fungi; N. J. Agr. Exp. Sta., Bui. 270, 1914. 

Kopeloff, N., The Effect of Soil Reaction on Ammonification by 
Certain Soil Fungi; Soil Sci., Vol. V, No. 1, pp. 541-574, 1916. 

Coleman, D. A., Environmental Factors Influencing the Activity of 
Soil Fungi; Soil Sci., Vol. V, No. 2, pp. 1-66, 1916. 

Brown, P. E., The Importance of Mold Action in Soil; Science, N. S., 
Vol. XLVI, No. 1182, pp. 171-175, 1917. 

Conn, H. J., The Microscopic Study of Bacteria and Fungi in Soil; 
N. Y. State Agr. Exp. Sta., Tech. Bui. 64, 1918. 



SOIL ORGANISMS 389 

in the surface soil. While the microscopic algas are probably- 
present in soils, it has never been shown that they are of 
practical importance. 

213. Actinomyces. — The aetinomyces are a filamentous 
form of organisms, widely distributed in nature and are prob- 
ably more nearly related to the bacteria than to the molds, 
although they produce spores and develop into branching 
forms of considerable complexity. Their production of aerial 
hyphaB is quite unlike the habits of bacteria. These thread 
organisms exist in the soil in both the vegetative and the 
resting stage and often make up quite a large proportion of 
the soil flora. They are extremely difficult to study, since 
they produce hard compact growths. It is questionable also, 
whether the growths produced artificially are exactly like 
those occurring in the soil. 

Hiltner and Stormer ^ found that 20 per cent, of the soil 
organisms developing on gelatin plates inoculated from the 
soil were aetinomyces. Conn ^ reports a range from 11 to 75 
per cent, under similar cultural conditions. The average was 
38 per cent. Conn estimates that 20 per cent, of the average 
flora consists of aetinomyces. The organisms were generally 
greater in meadow soil than in cultivated land, indicating 
the relationship of these thread forms to cellulose decomposi- 
tion. McBeth ^ found aetinomyces of wide distribution in 
soils and he concludes that they are undoubtedly an impor- 
tant factor in the decomposition of the cellulose of the soil 
organic matter. 

* Hiltner, L., and Stormer, K., Studien iiber die Bakterienflora des 
Ackerbodens ; Kaiserliches Gesundheitsamt, Biol. Abt. Land-u. Forstw., 
Bd. 3, S. 445-545, 1903. 

^ Conn, H. J., A Possible Function of Actinomycetes in Soil; Jour. 
Bact., Vol. 1, No. 2, pp. 197-207, 1916. 

^ McBeth, I. G., Studies on the Decomposition of Cellulose in Soils; 
Soil Sci., Vol. I, No. 5, pp. 437-487, 1916. Also, 

Waksman, S. A., and Curtis, R. E., The Actinomyces of the Soil; 
Soil Sci., Vol. 1, No. 2, pp. 99-134, 1916. 

Waksman, S. A., Cultural Studies of Species of Actinomyces; Soil 
Sci., Vol. VIII, No. 2, pp. 71-207, 1919. 



390 NATURE AND PROPERTIES OF SOIL 

214. Bacteria. — Of the several forms of micro-organisms 
in the soil, bacteria are probably the most important. In fact, 
the abundant and continued growth of higher plants on the 
soil is absolutely dependent on the presence of bacteria. 
Through their action chemical changes are brought about 
which result in the solution of both organic and inorganic 
material necessary for the life of higher plants, and which, 
in part at least, would not otherwise be available. 

Bacteria are single cell organisms and are probably the 
simplest forms of life with which we have to deal. They are 
generally much smaller than yeasts, multiplying by elongat- 
ing and dividing into half. They are, therefore, often called 
fission fungi. Molds multiply by budding. The activities of 
both groups are similar, in that they produce their effects 
very largely by the production of enzymes.^ The importance 
of enzymic influences must constantly be borne in mind in all 
biological transformations in the soil. 

Bacteria are very small, the larger individuals seldom ex- 
ceeding one or two microns (.001 to .002 m.m.) in diameter. 
In the soil there is good reason to suppose that there are 
many groups which are too small to be seen under the micro- 
scope. Such organisms may, therefore, function as a part of 
the colloidal matter of the soil. Many of the soil bacteria 
are equipped with extremely delicate vibrating hairs called 
flagella, which enable the organisms to swim through the 

^ Bacteria, as well as most fungi, bring about their important trans- 
formations largely by means of enzymes. These enzymes are catalytic 
agents and are generally considered as colloidal in nature. A number of 
transformations may be accelerated by enzymes, the exact reaction de- 
pending on the nature of the enzyme itself. The change in the soil of 
ammonia (NH3) to the nitrate form (NO3) is an example of oxidation 
and is spoken of as nitrification. The reversal of this action is desig- 
nated as reduction and is probably not entirely enzymic. A splitting 
action is very common. The breaking up of glucose into alcohol and 
carbon dioxide is an example of this (GsH^Oa = 2C2H5OH -f 2C0a). 
A fourth reaction that may be hastened by enzymic influence is hydrol- 
ysis. Cane-sugar may thus quickly produce glucose and fructose 
(C^H^Oi, -f H,0 = CH^ae + C,H,,Oa). 



SOIL ORGANISMS 391 

soil-water. The shape of bacteria is varied in that they may 
be nearly round, rod-like, or spirals. In the soil the rod- 
shaped organisms seem to predominate. 

As already stated, the primary method of multiplication 
of bacteria is by simple division, the process being very rapid 
under favorable conditions. The phenomena frequently takes 
place in thirty minutes. This almost unlimited capacity to 
increase in numbers is extremely important in the soil since 
it allows certain groups quickly to assume their normal func- 
tions under favorable conditions, even though their numbers 
were originally small. ^ Bacteria may thus be considered as 
a force of tremendous magnitude in the soil, held more or 
less in check by conditions, but ever ready to exert an influ- 
ence of profound importance on crop growth. 

In the soil bacteria probably exist as mats or clumps, 
called colonies, on and around the soil particles wherever food 
conditions are favorable. Natural and artificial forces tend 
to break up these colonies and, as many groups are flagellated, 
bacteria becomes well distributed through the soil. In gen- 
eral the greatest numbers are found in the surface layers of 
the soil, since conditions of temperature, aeration, and food 
are here more favorable. Many of the soil bacteria are able 
to produce spores, thus presenting both a resting and a vege- 
tative stage. The production of spores is often extremely 
important as it allows the organisms to survive unfavorable 
conditions of many kinds. 

The number of bacteria present in soil is quite variable as 
many conditions markedly affect their growth. The meth- 
ods - of determining the numbers are extremely inaccurate, 

^ If a single bacterium and every subsequent organism produced sub- 
divided every hour, the offspring from the original cell would be about 
17,000,000 in twenty-four hours. In six days the organisms would greatly 
surpass the earth in volume. Under actual conditions such multiplication 
would never occur, due to lack of food and other limitations. 

^ The counting of soil bacteria is generally carried out somewhat as 
follows: A small sample of soil (usually .5 gram) is placed in a sterile 
Erlenmeyer flask and treated with 100 cc. of sterile water. The sample 



392 NATURE AND PROPERTIES OF SOILS 

since many organisms cannot grow in the artificial media 
commonly used. Moreover, it is almost impossible to break 
up the clump of colonies in such a way as to determine the 
number of individuals present. It is fairly certain, however, 
that the numbers of bacteria in soil are very large, possibly 
ranging from 500,000 to 100,000,000 to a gram of dry soil. 
Gk)od soils seem, in general, to carry the greatest numbers. 
The bacterial flora, as well as the other soil organisms, fluctu- 
ate markedly with season, the numbers usually being great- 
est in the summer months. 

215. Conditions affecting bacterial growth.^ — Many con- 
is then well shaken in order to produce a suspension containing the 
bacteria originally present in the soil. Dilutions of 1 to 20,000, 1 to 
100,000 and 1 to 200,000 based on the original soil sample are made. 
Gelatin or agar plates are then inoculated, three from each dilution. 
After adequate incubation the colonies on the plates are counted, each 
colony supposedly representing one original organism. The numbers of 
bacteria that were present in the original soil are then calculated. The 
agar or gelatin of the plates generally receive a sterile extract from the 
soil together with certain added materials, organic or inorganic, in order 
that the growth of the bacteria may be hastened. 

Such a count does not represent by any means all of the bacteria of 
the soil, as some groups will not develop at all, while others require 
special media. Slowly growing groups of organisms, that would prob- 
ably appear if time were given, escape the count, since the plates are so 
quickly covered by more abundant growths. The suspension from the 
soil, used to inoculate the plates, does not contain all of the organisms 
aa single individuals, since it is impossible completely to break down the 
clump formation. This tends to make the counts too low. Special 
media and technique are of course necessary in studying fungi, algae 
and actinomyces. 

' Eahn, Otto, The Bacterial Activity in Soil as a Function of Grain-size 
and Moisture Content; Mich. Agr. Exp. Sta., Tech. Bui. 16, 1912. 

Plummer, J. K., Some Effects of Oxygen and Carbon Dioxide on Nitri- 
fication and Ammonification in Soils; Cornell Agr. Exp. Sta., Bui. 384, 
1916. 

Greaves, J. E., and Carter, E. G., Influence of Barnyard Manure 
and Water Upon the Bacterial Activities of the Soil; Jour. Agr. Ees., 
Vol. VI, No. 23, pp. 889-926, 1916. 

Brown, P. E. The Influence of Some Common Humus-forming Mate- 
rials of Narrow and of Wide Nitrogen-carbon Ratio on Bacterial Num- 
bers; Soil Sci., Vol. 1, No. 1, pp. 49-75, 1916. 

Waksman, S. A., Bacterial Numbers in Soils, at Different Depths and 
in Different Seasons of the Year; Soil Sci., Vol. I, No. 4, pp. 363-380, 
1916. 

Gainey, P. L., The Effect of Time and Depth of Cultivating a Wheat 



SOIL ORGANISMS 393 

ditions of the soil affect the growth of bacteria. Among the 
most important of these are the supply of oxygen and mois- 
ture, the temperature, the presence of organic matter, and 
the acidity or the basicity of the soil. 

All soil bacteria require for their growth a certain amount 
of oxygen. Some bacteria, however, can continue their activ- 
ities with much less oxygen than can others. Those requir- 
ing an abundant supply of oxygen have been called aerobic 
bacteria, while those preferring little air are designated as 
anaerobic bacteria. This is an important distinction, because 
those bacteria that are of greatest benefit to the soil are, in 
the main aerobes, and those that are injurious in their action 
are chiefly anaerobes. However, it seems likely that an 
aerobic bacterium may gradually accommodate itself within 
certain limits to an environment containing less oxygen, and 
an anaerobic bacterium may accommodate itself to the pres- 
ence of a larger amount of oxygen. It is quite possible that 
the aerobic and anaerobic organisms function in the soil at 
the same time, since a portion even of a well aerated soil is 
always highly charged with carbon dioxide. It is not improb- 
able, also, that there exists a more or less beneficial inter- 
relation between the two general groups. 

Bacteria require moisture for their growth, optimum water 
for higher plants seemingly being the best moisture for the 
development and activity of favorable soil organisms of all 
kinds. With a decrease of moisture the soil becomes well 
aerated, while an excessive water supply tends to encourage 
anaerobic conditions. Moisture, when aeration and tempera- 
ture are favorable, seems to be the main control of biological 
changes within the soil. 

Soil bacteria, like other plants, continue life and growth 

Seed-Bea upon Bacterial Activity in tJie Soil; Soil Sci., Vol. II, No. 2, 
pp. 193-204, 1916. 

Greaves, J. E., and Carter, E. G., Influence of Moisture on the Bac- 
terial Activities of the Soil; Soil Sci., Vol. X, No. 5, pp. 361-387, 1920. 



394 NATURE AND PROPERTIES OF SOILS 

under a considerable range of temperature. Freezing, while 
rendering bacteria dormant, does not kill them, and growth 
begins slightly above that point.^ It has been shown that 
some nitrification occurs at temperatures as low as from 37° 
to 39° F. It is not, however, until the temperature is con- 
siderably higher that bacterial functions are pronounced. 
From 70° to 110° F. their activity is greatest, and it dimin- 
ishes perceptibly below or above those points. The thermal 
death point of most forms of bacteria is between 110° and 




Fig. 56. — Some important decay organisms found in soils, (a), Acti- 
nomyces threads; (b), a colony of Actinomyces ; (e) and (d), Pro- 
teus vulgaris; (e), B. fluorescens; (f), B. subtilis. 

160° F., but the spore forms even resist boiling. Only in 
some desert soils does the natural temperature reach a point 
sufficiently high actually to destroy bacteria, and there only 
near the surface. In fact, it is very seldom that soil tempera- 
tures, other conditions being favorable, become sufficiently 
high to curtail bacterial activity. 

The presence of a certain amount of organic matter is es- 
sential to the growth of most, but not all, forms of soil bac- 

* In the seasonal study of bacteria it has been repeatedly noticed that 
the counts increased during the winter, especially after a freeze followed 
by a thaw. It was considered for a time that a special winter flora was 
present, and was able to multijvly in the soil-water which failed to freeze. 
It is now considered that this increase is only apparent, the freezing 
having disrupted the bacterial clumps, thus increasing the number of 
colonies appearing on the plates during incubation. 



SOIL ORGANISMS 395 

teria. The organic matter of the soil, consisting as it does of 
the remains of a large varietj^ of substances, furnishes a suit- 
able food supply for a very great number of forms of organ- 
isms. The action of one set of bacteria on the cellular matter 
of plants embodied in the soil produces compounds suited to 
other forms, and so from one stage of decomposition to another 
this constantly changing material affords sustenance to bac- 
terial flora, the extent and variety of which it is difficult to 
conceive. A soil low in organic matter usually has a lower 
bacterial content than one containing a large amount, and, 
under favorable conditions, the beneficial action, to a certain 
point at least, increases with the content of organic substance ; 
but, as the products of bacterial life are generally injurious 
to the organisms producing them, such factors as the rate 
of aeration and the basicity of the soil must determine the 
effectiveness of the organic matter. 

The so-called acidity of the soil is probably as important 
a factor in bacterial activity as it is to higher plants.. In 
general, favorable soil organisms of all kinds seem to func- 
tion better in a soil carrying sufficient active base to generate 
conditions favorable for higher plants. An exception some- 
times occurs, however, notably in the case of the "finger-and- 
toe" disease of certain CruciferaB, which is retarded by 
liming. 

The activities of many soil bacteria result in the formation 
of acids which are injurious to the bacteria themselves, and 
unless there is present some base with which these can com- 
bine, bacterial development is inhibited by such products. 
This is one of the reasons why lime is so often of great benefit 
when applied to soils, and especially to those on which alfalfa 
and red clover are growing. For the same reason the 
presence of lime hastens the decay of organic matter in 
certain soils, and the conversion of nitrogenous material 
into compounds available to the plants. As showing the 
value of lime in the process of nitrate formation it has been 



396 NATURE AND PROPERTIES OF SOILS 

pointed out that in the presence of an adequate supply of 
calcium the availability of ammonium salts is almost as high 
as that of nitrate salts, but where the supply of calcium is 
insuflficient the value of ammonium salts is relatively low. 

216. Organisms injurious to higher plants. — While the 
macro-organisms may, under certain conditions, be detri- 
mental to the growth of higher plants, it is the smaller in- 
habitants of the soil that attract especial attention in this re- 
spect. While protozoa may, under special circumstances, be 
extremely detrimental, injurious organisms are confined 
mostly to fungi and bacteria. They may be entirely parasitic 
in their liabits or only partially so, while they may injure 
higher plants by attacking the roots or even the tops. Those 
that infest parts of the plant other than the roots are not 
strictly soil organisms, as they pass only a part of their 
cycle in the soil. Some of the more common diseases pro- 
duced by soil organisms are : wilt of cotton, cowpeas, water- 
melon, flax, tobacco, tomatoes, and other plants; damping-off 
of a large number of plants ; root-rot ; and galls. 

Injurious fungi or bacteria may live for long periods in 
the soil, if the conditions necessary for their growth are main- 
tained. Some of them will die within a few years if their host 
plants are not grown on the soil, but others are able 'to main- 
tain existence on almost any organic substance. Once a 
soil is infected it is likely to remain so for a long time, or 
indeed indefinitely. Infection easily occurs. Organisms from 
infected fields may be carried on implements, plants, or rub- 
bish of any kind, in soil used for inoculation of leguminous 
crops, or even in stable manure containing infected plants 
or in the feces resulting from the feeding of such plants. 
Flooding of land by which soil is washed from one field to 
another may be a means of infection. 

Prevention is the best defense from diseases produced by 
such soil organisms. Once a disease has procured a foothold, 
it is often impossible to eradicate all its organisms. Rota- 



SOIL ORGANISMS 397 

tion of orops is effective for some diseases, but entire absence 
of the host crop is often necessary. The use of lime is bene- 
ficial in the case of certain diseases. Chemicals of various 
kinds have been tried with little success. Steam sterilization 
is a practical method of treating greenhouse soils for a num- 
ber of diseases. The breeding of plants immune to the dis- 
ease affecting its particular species has been successfully car- 
ried out in the case of the cowpea and cotton, and can doubt- 
less be accomplished with others. 

In regions in which farming is confined largely to one 
crop or to a limited number of cereals, it is the common ex- 
perience that yields decrease greatly in the course of a score 
of years after the virgin soil is broken. The cause for this 
is attributed by Bolley,^ in large measure, to a diseased con- 
dition of the plants, due to the growth of various fungi that 
inhabit the soil and attack the crops grown on it. He reports 
that he experimented with pure cultures taken from wheat 
grains, straw, and roots, and has demonstrated that certain 
strains or species of Fusarium, Helminthosporium, Alter- 
naria, Macrosporium, Colletotrichum, and Cephalothecium 
are directly capable of attacking and destroying growing 
plants of wheat, oats, barley, brome-grass, and quack-grass, 
and that within limits the disease may be transferred from 
one type of crop to another. 

217. The beneficial influences of soil organisms. — While 
the macro-organisms of the soil are usually beneficial to 
higher plants, the more important relationships are occupied 
by the micro-organisms. The micro-organisms of the soil take 
an active part in removing dead plants and animals from the 
surface of the land, and in bringing about the other oper- 
ations that are necessary for the production of higher plants. 
The first step in preparation for plant growth is to remove the 
remains of plants and animals that would otherwise accumu- 
late to the exclusion of higher plants. These are decomposed 

^ BoUey, H. L., Wheat; N. Dak. Agr. Exp. Sta., Bui. 107, 1913. 



398 NATURE AND PROPERTIES OF SOILS 

through the action of organisms of various kinds, the inter- 
mediate and final products of decomposition assisting plant 
production by contributing nitrogen, and certain mineral 
compounds that are a directly available source of plant nutri- 
ents, and also by the effect of certain of the decomposition 
products on the mineral substances of the soil, by which they 
are rendered soluble and hence available to plants. 

Through these operations the supply of carbon and nitro- 
gen required for the production of organic matter is kept in 
circulation. The complex organic compounds in the bodies 
of dead plants or animals, in which condition higher plants 
cannot use them, are, under the action of micro-organisms, 
converted by a number of stages into the simple compounds 
used by plants. In the course of this process, a part of the 
nitrogen is sometimes lost into the air by conversion into free 
nitrogen, but fortunately this may be recovered and even 
more nitrogen taken from the air by certain other organisms 
of the soil. 

Higher fungi and actinomyces are particularly active in 
the early stages of decomposition of both nitrogenous and 
non-nitrogenous organic matter. Molds are capable of am- 
monifying proteins, and even re-forming complex protein 
bodies from the nitrogen of ammonium salts. Certain of the 
molds and of the algee are apparently able to fix atmospheric 
nitrogen, and contribute in addition a supply of carbohy- 
drates required for the use of the nitrogen-fixing bacteria. 
While the higher fungi are important in such transforma- 
tions, their activities in almost every stage are excelled by 
those of the bacteria. Because of this, the vital biological 
transformations within the soil are generally ascribed to bac- 
terial action, the bacteria receiving the greatest attention of 
the numberless organisms making up both the soil flora and 
fauna. 

218. Biological cycles. — ^Because of a lack of knowledge 
regarding the flora and fauna of the soil, it is obviously im- 



SOIL ORGANISMS 399 

possible to discuss in detail the transformations caused by 
individual species of organisms or even by groups of related 
species. From the standpoint of soil fertility such an at- 
tempt is unnecessary, as a practical understanding of the 
changes through which a given soil constituent passes as 
it is prepared for plant nutrition, is much more important 
than the possession of specific knowledge regarding the organ- 
isms concerned. As a consequence it has become customary 
to discuss the biological transformations of the more impor- 
tant soil constituents, including as much regarding the speci- 
fic organisms and groups of organisms involved as is con- 
sistent with a clear fertility viewpoint.^ Four cycles are gen- 
erally recognized, as follows: (1) the carbon cycle, (2) the 
sulfur cycle, (3) the mineral cycle, and (4) the nitrogen 
cycle. 

219. The carbon cycle. — Since all organic compounds 
carry carbon, nitrogenous as well non-nitrogenous materials 
are involved in the carbon cycle. Nevertheless attention will 
be directed for the time being only toward the carbon and the 
changes that it undergoes from the time it enters the soil 
until it is removed either by aeration, leaching, or by plant 
absorption. 

Most of the carbon compounds enter the soil as plant tissue, 
although animal remains contribute appreciable amounts. 
These carbonaceous materials are immediately attacked in the 
soil by a host of different organisms capable of producing 
fermentation. While such bacteria as Bacillus suhtilis, Ba- 
cillus mycoides, and the like have a great deal to do with the 
decay processes, they are by no means the only agents. Most 
of the microscopic fungi, as well as the larger fungi and algae, 

^ There are two general ways of studying the soil flora. A classification 
of the organisms may be attempted. This requires the isolation and 
study of individuals and has so far met with but little success. The 
second approach is a biochemical one, in which the transformations oc- 
curring in the soil are studied first, the specific organisms involved being 
a secondary consideration. The determination of the capacity of the 
soil to produce ammonia is an example of this method of study. 



400 NATURE AND PROPERTIES OF SOILS 

aid in the initial transformation, being particularly effective 
in decomposing cellulose. The actinomyces, present in such 
large numbers, seem to be especially fitted for the breaking 
down of such resistant material. 

The result of these complex decomposition processes is the 
formation of a partially decayed group of carbon-bearing 
material, some being quite simple while others are extremely 
complicated. The change is accompanied through its entire 
course by the formation of carbon dioxide and water, the end- 
products of carbohydrate decay. The same heterogeneous 
group of soil organisms, which initiate the simplification of 
carbonaceous materials, seem to continue the process until 
only the end products and the more resistant portions of the 
original tissue remain. 

The transformations above discussed are not the only 
sources of carbon dioxide within the soil. Some carbon diox- 
ide is brought down in rain-water, while still more is given off 
by the roots of living plants (see par. 156). Moreover some 
carbon dioxide is obtained from the inorganic matter of the 
soil, especially if the land has recently received an applica- 
tion of limestone. The reactions within the soil seem to de- 
compose such carbonates rather readily, carbon dioxide being 
given off (see par. 201). 

220. The loss of carbon from the soil. — Carbon diox- 
ide, the importance of which has already been fully discussed 
(par. 132), may suffer transformation in a number of ways 
in the soil. It may be lost (1) to the atmospheric air; (2) 
it may react with the mineral constituents of the soil and be 
held at least temporarily by the soil mass; or (3) it may be 
removed by leaching. Since the soil-water is always more or 
less charged with carbon dioxide and since 'it carries car- 
bonate and bicarbonate salts, considerable carbon is continu- 
ally being removed in this way. In this regard the figures 
from the Cornel lysimeter tanks ^ are especially interesting. 

^ Unpublished data. Cornell Agr. Exp. Sta., Ithaca, N. Y. 



SOIL ORGANISMS 



401 



The data are expressed in pounds to the acre and are averages 
of ten years' experimentation. The carbon was lost as the 
bicarbonate, only traces of carbonates being present. (See 
table LXXXVlil, page 402). 



AHIMAL- 



TO 
ATMOSPHERE 




"y/miW^^^ GREEN FARM 

MANURE MANURE 



SOIL 
REACTIONS 



^^^-. V j/ 



OECAY 
PARTIALLY DECOMPOSED 
MATERIALS 



OTHER BIOLOGICAL 
■ACTIVITIES 



LEACHING 
LOSSES 



CHEMICAL 
REACTIONS 



Fig. 57. — Diagram showing the transformations of carbon, commonly 
spoken of as the ' ' carbon cycle. ' ' 



It is apparent that a drainage loss of about 1200 pounds 
of bicarbonate (HCO3) may be expected each year to the 
acre, without considering the carbon dioxide which is respired 
to the atmosphere. This latter loss probably at least equals, 
if it does not greatly exceed, the loss of carbon in the bicar- 
bonate form. Together they cause a disappearance of several 
hundred pounds of carbon a year under the conditions main- 



402 NATURE AND PROPERTIES OF SOILS 

Table LXXXVIII 

loss of carbon from the soil in drainage, expressed in 
pounds to the acre per year. cornell lysimeters. 



Treatment 


HCO3 

(pounds) 

1391 
1350 
1193 


Carbon 
(pounds) 


Bare soil 

Rotation 

Grass 


273 
265 
234 







tained in the Cornell lysimeters. The application of two tons 
of green-manure to the acre would be necessary to replace 
even the drainage loss cited above. 

Small amounts of carbon may be removed by means other 
than drainage or diffusion into the atmospheric air. Nu- 
merous investigators ^ have shown that plants are capable 
of assimilating various organic materials. Recently it has 
been demonstrated that higher plants may utilize a consid- 
erable variety of carbohydrate compounds.- Such materials, 
when thus assimilated, no doubt supply the plant with en- 
ergy and thus are foods rather than nutrients. The ready 
response of certain crops, such as maize, to applications of 
farm manure lends plausibility to the theory that considerable 
carbon may be removed from the soil by plants and that the 
carbon dioxide of the air is not the only immediate source of 
the element carbon. 

221. The sulfur cycle. — Sulfur is an essential plant nu- 

^ Hutchinson, H. B., and Miller, N. H. J., The Direct Assimilation of 
Inorganic and Organic Forms of Nitrogen by Higher Plants; Centrlb. f. 
Bakt., II, Band 30, S. 513-547, 1911. 

^ Maze, P., Influence, sur le developpement de la plante, des substances 
minerales qui s'accumulent dans ses organes coming residus d' assimila- 
tion ; Compt. Eend. Sci., Paris, Tome 152, pp. 783-785, 1911. 

Eavin, P., Nutrition carbonee des plantes a I'aide des acides organique 
libres et combines; Ann. Sci. Nat. Bot., Ser. 9, No. 18, pp. 289-446, 
1913. 

Kniidson, L., Influence of Certain Carbohydrates on Green Plants; 
Cornell Agr. Exp. Sta., Memoir 9, July 1916. 



SOIL ORGANISMS 403 

trient, being utilized by such erops as alfalfa, 'tuniips, and 
cabbage in much larger amounts than is pliosphorus. Al- 
thougli sulfur probably seldom becomes a limiting factor in 
crop production (see par. 264), where rational methods of 
soil management are practiced, its transformations in the soil 
are of great importance. 

Sulfur is absorbed by the plant as the sulfate ion and con- 
sequently all forms of soil sulfur must be changed to the sul- 
fate before the plant may benefit to any degree. This trans- 
formation of sulfur, both organic and inorganic, to the sul- 
fate form, insofar as it is biological, has been termed by 
Lipman,^ sulfofication. The reactions involved after hydro- 
gen sulfide or free sulfur are formed may be written as fol- 
lows: 

2H,S + 30o = 2H,S03 

S -h H,0 -h O. = HoSOy 

H0SO3 + CaH.CCOg), = CaSOa + 2HoO -f 2CO2 

2CaS03 + O2 = 2CaS04 

"While the oxidation reactions cited above are not entirely 
biological, purely chemical changes occurring to a slight de- 
gree, the decay processes preceding them are due wholly to 
bacteriological and allied influences. The organisms involved 
in sulfofication are probably many, including the higher forms 
of fungi as well as bacteria. The organisms that function in 
the carbon cycle no doubt are active in the sulfur transfor- 
mations as well. 

The possible sources of the sulfur which is found in the 
sulfur cycle are four: (1) plant and animals tissue, (2) fer- 
tilizers, (3) rain-water, and (4) the inorganic sulfur of the 
soil itself. The organic source is probably the most impor- 
tant means by which the sulfur supply of the soil is aug- 
mented in practice. The addition of farm manure and the 
turning under of crop residues and green-manures will do 

^Ldpmaii, G. J., Suggestions Concerning the Terminology of Soil 
Bacteria; Bot. Gaz,, Vol. 51, pp. 454-460, 1911. 



404 NATURE AND PROPERTIES OF SOILS 

much to retard the sulfur reduction which is constantly oc- 
curring. Fertilizers, such as acid phosphate, ammonium sul- 
fate, and potassium sulfate, may also be valuable sources of 
sulfur. The amount of sulfur carried down in rain-water is 
largely in the sulfate form and is quite variable, ranging from 
a few pounds of SO3 yearly to the acre to over 160 pounds. 
The rainfall addition at Ithaca,^ New York, is about 65 
pounds of SO3 to the acre a year, while Stewart - reports a 
yearly gain to the acre of 113 pounds at the University of 
Illinois. The inorganic sulfur of the soil also constantly 
tends to enter the sulfur cycle and must be reckoned with in 
any study of sulfofication. 

222. Loss of sulfur from the soil. — The loss of sulfur 
from the soil under normal agricultural conditions occurs 
in two ways: (1) losses in drainage, and (2) removal by 
cropping. Unless such losses can adequately be met by ad- 
ditions of sulfur or sulfur compounds, it is obvious that this 
element will become a limiting factor in crop growth. The 
figures ^ from the Cornell lysimeters are very instructive in 
this regard. The soil used was a Dunkirk silty clay loam. 



Table LXXXIX 

average annual loss of sulfur (as so3) by percolation 
and cropping. cornell lysimeters. average of 10 years. 





Pounds to the Acre of SO3 Lost Through 




' Drainage 


Crop 


Total 


Bare soil 

Rotation 


132.0 
108.5 
111.0 




132.0 
149.5 


41.0 

29.2 


Grass 


140.2 







1 Wilson, B. D., Sulfur Supplied to the Soil in Jiain Water; Jour. 
Amer. Soc. Agror.., Vol. 13, No. 5, pp. 226-229, 1921. 

^Stewart, R., Sulfur in Relation to Soil Fertility; 111. Agr. Exp. Sta., 
Bui. 227, 1920. 

3 Unpublished data, Cornell Agr. Exp. Sta., Ithaca, N. Y. 



SOIL ORGANISMS 405 

Since the sulfur added to the soil at Ithaca, New York, 
amounts to only 65 pounds of SO3 yearly to the acre, other 
sources of sulfur assume considerable importance in fertility 
practice. It seems probable, however, that the judicious 
use of fertilizers carrying sulfur in conjunction with farm 
manure, green-manure and crop residues, will adequately 
care for the sulfur needs of the average soil (see par. 264). 

223. Factors influencing sulfofication. — The sulfofying 
activities of the soil flora are greatly influenced by conditions 
within the soil. Brown ^ has found that the addition of farm 
manure and green-manure greatly stimulates sulfofication, al- 
though carbohydrates alone seem to exert a depressing influ- 
ence. Lime, unless applied in veiy large amounts, encour- 
aged the transformation of the sulfur compounds, increas- 
ing the amount of sulfates present in the soil. The reason 
for this influence is evident from the reactions already quoted. 
The partial oxidation of hydrogen sulfide or of free sulfur 
produces sulfurous acid (H0SO3), which exerts a retarding 
influence on further action, unless a base, such as calcium or 
magnesium, is present to form a salt of this acid. 

Brown's results also indicate the preponderant influence 
of aeration, moisture, and organic matter on sulfofication. 
Optimum conditions for crop growth, as far as these factors 
are concerned, seem also to be optimum for the transforma- 
tion of sulfur compounds in the soil. These same conditions 
also favor satisfactory reactions within the carbon cycle as 
well. 

^ Brown, P. E., and Kellogg, E. H., The Determination of the Sul- 
fofying Power of Soils; Jour. Biol. Chena., Vol. XXI, No, 1, pp. 73-89, 
1915. 

Brown, P. E., and Johnson, H. W., Studies in Sulfofication ; Soil Sci., 
Vol. I, No. 4, pp. 339-362, 1916. 

Brown determines the sulfofying power of soil by adding .1 gram of 
Na2S or free sulfur to 100 grams of fresh soil, adjusting the' moisture 
content to optimum and incubating from five to ten days. The sulfates 
are then determined by shaking the soil with water for seven hours, 
filtering and precipitating the sulfates with barium chloride. The 
amounts of sulfates are estimated in a sulfur photometer. An untreated 
sample of soil should be run as a check. 



406 NATURE AND PROPERTIES OF SOILS 

224. The sulfur compost. — It has been noted by a num- 
ber of experimenters that the presence of sulfur compounds 
in the soil and especially elemental sulfur tends to develop 
considerable acidity. The cause of this acidity has already 
been explained. In 1916, Lipman ^ and his co-workers sug- 
gested that a practical use be made of sulfofication in ren- 
dering certain mineral nutrients, such as potash and phos- 
phoric acid, available. Lipman devised a compost of sulfur 
and raw rock phosphate. His results seem to indicate that 
sufficient acid might be formed by biological oxidation ap- 
preciably to influence the solubility of the rock phosphate. 

Brown and Warner - later used a compost of sulfur, farm 
manure and raw rock phosphate. Remarkable increases in the 
solubility of phosphoric acid, measured by extraction with 
a solution of ammonium citrate, were recorded. The results 
of Lipman, Brown, and Warner have been corroborated by 
Ames and Richmond,^ and Shedd.* Ames and Boltz ° in 
1919 found that sulfur composted with feldspar appreciably 
influenced the solubility of potash. Such results as those 
recorded above indicate the importance of sulfofication in 
the soil under ordinary circumstances, as well as a possible 
value in a more intensified procedure. 

The practicability of using sulfur composts on the farm 

^ Lipman, J. G., et al., Sulfur Oxidation in the Soil and Its Effects on 
the Availabilitii of Mineral Phosplmtes; Soil Sci., Vol. II, No. 6, 
pp. 499-538, 1916. 

^ Brown, P. E., and Warner, H. W., Production of Available Phos- 
phorus from Bock-Phosphate by Composting with Sulfur and Manure; 
Soil Sci., Vol. IV, No. 4, pp. 269-282, 1917. 

^Ames, J. W., and Richmond, T. E., Effect of Sulfofication and 
Nitrification on Bock Phosphate ; Soil Sci., Vol. VI, No. 4, pp. 351-364 
1918. 

■"Shedd, O. M., Effect of Oxidation of Sulfur in Soils on the Solu 
hility of Bock -Phosphate and on Nitrification; Jour. Agr. Res., Vol 
XVIII, No. 6, j^p. 329-345, 1919. 

^ Ames, J. W., and Boltz, G. E., Effect of Sulfofication and Nitrifica 
tion on Potassium and Other Soil Constituents ; Soil Sci., Vol. VII 
No. 3, pp. 183-195, 1919. See also, Tottingham, W. E., and Hart, E. B. 
Sulfur and Sulfur Composts in Belation to Plant Nutrition; Soil Sci. 
Vol, XI, No. 1, pp. 49-65, 1921. 



SOIL ORGANISMS 407 

is yet to be determined, and will depend on a number of fac- 
tors. The soil must, of course, be deficient in the constituent 
composted with sulfur. Otherwise, an application of sulfur 
alone would give just as good results. Again the cost of 
composting must be reckoned with. It yet remains to be 
proven by crop growth whether the efficiency of sulfur is any 
greater Avhen it is composted with such materials as raw rock 
phosphate and farm manure and applied to the soil, than 
when these materials are added separately. 

225. The mineral cycle. — The strictly mineral constitu- 
ents of the soil seem to undergo as complex and intricate 
transformations as do the elements that are considered as 
more closely related to the soil organic matter, such as car- 
bon, nitrogen and sulfur. While a part of the mineral cycle 
is purely chemical or physico-chemical, the biological phase 
is by no means unimportant. In fact, were it not for the in- 
fluence of organisms within the soil, little or no mineral mat- 
ter, such as phosphoric acid and potash, would ever become 
available to higher plants. 

When plant or animal tissue enters the soil, it undergoes 
decay in the manner already described, the ash constituents 
being liberated and either utilized directly by higher plants 
again or converted into a part of the soil mass. The main 
source of the mineral nutrients for any plant is of course the 
inorganic portion of the soil rather than the organic part. 
It is thus necessary to investigate what influence, if any, soil 
organisms have on such material. 

The action of organisms on the inorganic portions of the 
soil is of two kinds: (1) direct, and (2) indirect. In the 
former the soil organisms themselves attack the mineral mat- 
ter, rendering part of it available. Some of this soluble ma- 
terial is absorbed by the organisms, becoming a part of the 
cell contents. When the fungus or bacterium dies, this ma- 
terial through decay again becomes available and may be 
used by higher plants. While most soil organisms probably 



408 NATURE AND PROPERTIES OF SOILS 

function to a certain extent in this direction, some are es- 
pecially active. It is known that B. my c aides, B. mesenteri- 
cus and B. megatherium are capable of assimilating phos- 
phorus in considerable quantities, while such organisms as 
Beggiotoa and Ophidomonas store up sulfur in large amounts. 
In the same way iron, potassium, calcium, and like elements 
may be utilized. While such biological action is at the time 
a direct competition with higher plants, more mineral ma- 
terial is ultimately available in the soil through such activ- 
ities. 

While the direct effects of organisms on soil minerals is 
no doubt very important, the direct influences seem to be 
more vital in a practical way. While this indirect influence 
may be in part enzymic, it is probably largely due to the 
production of carbon dioxide, which accompanies all types of 
life processes. The sulfurous acid and nitrous acid of the 
sulfur and the nitrogen cycles, respectively, are also active 
to a certain extent. The preceding discussion of the sulfur 
compost indicates how vigorous the biological oxidation with- 
in the sulfur cycle may become under certain conditions. In 
the soil, however, carbon dioxide is probably by far the most 
important.^ Since the significance of carbon dioxide has 
already been adequately discussed (pars. 17, 58 and 132), it is 
sufficient at this point to state that this gas, because of its 
large amounts and its intimate relationship to the mineral 
material, is probably the most effective solvent agent in the soil. 

* Typical reactions involving tri-calcium phosphate, orthoclase and cal- 
cium carbonate are as follows: 

Ca^CPO,)^ + 2C0, -t- 2H,0 = CsiJl^{VO,)^ -f Ca(HCOJj. 
2KAlSi30, + CO, + 2H2O = H.Al^iA + KjCO^ + 4SiO,. 
CaCOa + H,0 + CO, = CaCHCO,)^. 



CHAPTER XXI 
SOTL ORGANISMS— THE NITROGEN CYCLE 

Op the various nutrient materials applied to the soil for 
the use of plants nitrogen has the highest commercial value 
and is absorbed in very large quantities. Moreover, nitro- 
gen is lost from the soil in considerable amounts in drainage 
water and possibly to some extent in gaseous form. The 
great importance of this element and of its compounds in 
agriculture and the possibility of it becoming a limiting factor 
in crop production has lead to much study regarding its re- 
actions and movements in the soil. 

The original source of the world's supply of combined nitro- 
gen has been the atmosphere and, as the free gas is exceed- 
ingly inert,^ the natural forces which facilitate its combina- 
tion must be extremely powerful. The movement of nitrogen 
from air to soil, from soil to plant, from plant back to soil or 
to animal, and from animal to soil, with a return to air at 
various stages, involves many forces, many factors, many or- 
ganisms, and many reactions. These complicated changes 
are spoken of as the nitrogen cycle. 

226. The nitrogen cycle. — In tracing the various trans- 
formations through which the nitrogen passes, the conspicu- 
ous feature is the great complexity of the cycle. Apparently 
the nitrogen cycle is much more extended and intricate than 
either the carbon or sulfur cycles. This complexity, however, 

^ Because nitrogen is such an inert gas, it must not be inferred that it 
forms inactive compounds with other materials. In combination it is 
extremely active, seemingly being the basis of all plant and animal life 
processes. 

409 



410 NATURE AND PROPERTIES OF SOILS 

is more apparent than real. The transformation of nitro- 
gen has received so much attention and study that more 
is known regarding the changes involved. The other cycles 
are probably just as extended and complicated, the lack of 
knowledge forcing a simpler presentation. 

From the standpoint of soil fertility the compounds that 
are produced in the nitrogen cycle and the relation of these 
materials to plant growth are of major consideration. While 
the organisms involved in the transformation should receive 
as much attention as is practicable, the approach should be by 
means of biological-chemistry rather than through bacteri- 
ology. 

It must not be inferred that the carbon, sulfur and nitro- 
gen cycles are distinct or that transformations may proceed 
in one with no activity in the others. As a matter of fact, 
the cycles are interlocked in a hopelessly intricate manner. 
The decomposition of proteid matter involves all of the cycles 
already mentioned. The carbon, sulfur, and nitrogen un- 
dergo distinctly different transformations, but the changes 
are so closely related as to make definite lines of distinction 
very difficult. Proteid matter may produce urea, carbon 
dioxide, water, and sulfates. Certain of these products often 
strongly influence the solubility of the soil minerals. Thus, 
the four cycles already mentioned would be involved in the 
decomposition of one original compound. 

227. Decay and putrefaction.^ — The decomposition of 
most nitrogenous matter is very rapid in a normal soil, the 
putrefactive influences producing partially decayed sub- 
stances of great variety.- Some of these materials are very 
complicated, while others are capable of being absorbed di- 

* Decomposition and decay are general terms, referring to all types 
of biological degradation. Fermentation refers to the decomposition of 
carbohydrates, while putrefaction has to do with nitrogenous materials. 
The two latter terms are generally very loosely used. 

' Lathrop, E. C, Protein Decomposition in Soils; Soil Sci., Vol. I, 
No. 6, pp. 509-532, 1916. 



SOIL ORGANISMS 411 

rectly by plants without further change. Carbon dioxide and 
water are formed continuously as the process advances. The 
sulfur of the proteid compounds produces hydrogen sulfide 
or free sulfur and later sulfates. 

Hutchinson and Miller/ as well as other investigators, 
have studied the question of the assimilation of nitrogenous 
organic compounds by higher plants. The general conclu- 
sions indicate that such a source of nitrogen is quite impor- 
tant and sometimes allows the plant to benefit markedly from 
the assimilation of such materials. Maize, for example, seems 
to be particularly stimulated by farm manure, which carries 
large amounts of organic nitrogenous compounds such as 
urea. Acetamide, urea, barbituric acid, creatinine, alloxan, 
peptone, and a number of other organic compounds have 
been shown to be available to certain higher plants. 

Decay and putrefaction are carried on by a large number 
of organisms, the higher fungi as well as such bacteria as 
B. subtilis, B. mycoidtes, and similar micro-organisms engag- 
ing in the decomposition processes. Some of the charac- 
teristic, although not constant, products formed in the pu- 
trefaction of albumin and proteins are albumoses, peptones, 
and amino acids, followed by the formation of cadaverine, 
putrescine, skatol, and indol. Where an abundant supply 
of oxygen is present, or where a sufficient supply of carbo- 
hydrates exists, the latter substances are not formed. There 
are many other products of putrefaction, including a num- 
ber of gases, as carbon dioxide, hydrogen sulfide, marsh gas, 
phosphine, hydrogen, nitrogen, and the like. 

Present-day knowledge of the subject does not make it pos- 
sible to present a list of the organisms concerned in each step, 
or to name all the intermediate products formed. For the 
student of the soil the first consideration is a knowledge of 

^ Hutchinson, H. B., and Miller, N. H. J., The Direct Assimilation of 
Inorganic and Organic Forms of Nitrogen by Higher Plants; Centrlb. f. 
Bakt., II, Band 30, Seite 513-547, 1911. 



412 NATURE AND PROPERTIES OF SOILS 

the circumstances under which the nitrogen is made avail- 
able to plants, and the conditions that are likely to encourage 
its loss from the soil. 

228. Ammonification may be considered as the second step 
in the simplification which nitrogenous compounds undergo 
in the soil. As the name implies, it is the stage of the decay 
process in which ammonia is one of the important products. 
Like other processes of decomposition, there are many species 
of organisms capable of producing ammonia, the higher fungi 




Fig. 58. — Some soil organisms important in the nitrogen cycle, (a) 
Azotohacter agilis; (b) nitrate bacteria. Urea bacteria, (c) Uro- 
hacillus miguelii and (d) Urobacillus leubii. 

and algffi as well as bacteria participating in the change in the 
character of the nitrogen compounds. 

Different soil organisms display diverse abilities in con- 
verting the nitrogen of the same organic material into am- 
monia, some acting more rapidly or more thoroughly than 
others. In tests by certain investigators in which the same 
bacteria were allowed to act on different substances, the order 
of their efficiency was reversed with a change of substance. 
This characteristic preference of a class of organisms for the 
decomposition of certain substances is made evident by the 
experiments of Sackett,^ who found that in some soils dried 

'Sackett, W. G., The Ammonifying Efficiency of Certain Colorado 
Soils; Colo. Agr. Exp. Sta., Bui. 184, 1912. 



SOIL ORGANISMS 413 

blood was ammouified more rapidly than was cottonseed meal, 
while in other soils the reverse was true. 

While the soil fungi have been but little studied, the litera- 
ture available seems to indicate that they take an important 
part in all soil processes, except possibly the fixation of at- 
mospheric nitrogen and the formation of nitrates. Most soil 
fungi produce ammonia readily. Waksman ^ found such 
forms as Mucor racemosus, Pencillium lilacinum, and Rhiz- 
opus sp. II compared favorably in capacity to produce am- 
monia with Bacillus mycoidcs when grown in artificial cul- 
ture, blood and cottonseed meal being the sources of nitrogen. 
Kopeloff - found that certain fungi seemed to prefer an acid 
medium for their ammonifying activities. This suggests that 
a natural provision is thus made for ammonification, no mat- 
ter what the soil reaction may be. 

Among the bacteria producing ammonification are B. my- 
caides, B. subtilis, B. mesentericus vidgatus, B. janthinus, 
and B. proteus vulgaris. Of these, B. mycoides has been very 
carefully studied, and the findings of Marchal ^ may be taken 
as representative of the process of ammonification. He found 
that when this bacterium was seeded on a neutral solution of 
albumin, ammonia and carbon dioxide were produced, to- 
gether with small amounts of peptone, leucine, tyrosine, and 
formic, butyric, and propionic acids. He concludes that in 
the process atmospheric oxygen is used, and that the carbon 
of the albumin is converted into carbon doxide, the sulfur 
into sulfates, and the hydrogen partly into water, and partly 
into ammonia by combining with the nitrogen of the organic 

^Waksman, S. A., Soil Fungi mid Their Activities; Soil Sci., Vol. 
II, No. 2, pp. 103-155, 1916. See also, McLean, H. C, and Wilson, 
G. W., Ammonification Studies with Soil Fungi; N. J. Agr. Exp. Sta., 
Bui. 270, 1914. 

" KopeloflP, N., The Effect of Soil Eeaction on Ammonification by 
Certain Soil Fungi; Soil Sci., Vol. I, No. 6, pp. 541-573, 1916. 

'Marchal, E., Sur la Production de I'Ammoniaque dans le Sol par 
les Microbes; Bulletins de I'Acadc Eoyale de Belg., 3 series, T. 25, "pp, 
727-776; 1893. 



414 NATURE AND PROPERTIES OF SOILS 

substance. Marchal found that B. mycoidcs was also capable 
of ammonifying casein, fibrin, legumin, glutin, myosin, serin, 
peptones, creatine, leucine, tyrosine, and asparagine, but 
not urea. 

The following reactions may be cited as indicating the 
changes that probably occur when albumin and urea undergo 
ammonification : 

C,,H„,N,,SO,, + 770o = 29H2O -f 72CO2 + SO3 + I8NH3 
Albumin 

CONoH, + 2H2O = (NHJ2CO3 
Urea 

While ammonification ^ seems to proceed to the best advan- 
tage in a well-drained and aerated soil with plenty of active 
basic material present, it will take place to some extent under 
almost any condition, due to the great number of different or- 
ganisms capable of accomplishing the change. In certain 
soils, as shown by Russell and Hutchinson ^ as well as by 
other authors (see par. 211), protozoa may retard ammoni- 
fication by feeding on the chief ammonia-producing organ- 
isms. Such a condition is seldom serious in arable soils. 

^ The ammonifying efficiency of a soil is usually determined by treat- 
ing a 200-gram sample of fresh soil with cottonseed meal or dried blood 
carrying 120 milligrams of nitrogen. The mixture is then incubated, 
usually for seven days, at optimum temperature and moisture. The in- 
crease in ammonia is taken as a measure of the ammonifying efficiency. 
The artificial nature of the test detracts largely from its value. See 
Temple, J. C, TJie Value of Ammonification Tests; Ga. Agr. Exp. Sta., 
Bui. 126, 1919. 

^ RuSfeell, E. J., and Darbishire, F. V., Oxidation in Soils and Its 
Belation to Productiveness. Part 2. The Influence of Partial Steriliza- 
tion; Jour. Agr. Sci., Vol. 2, pp. .305-326, 1907. 

Russell, E. J., and Hutchinson, H. B., TJie Effect of Partial Sterilisa- 
tion of Soil on the Production of Plant Food; Jour. Agr. Sci., Vol. 3, 
pp. 111-144, 1909. 

Russell, E. J., and Hutchinson, H. B., The Limitation of Bacterial 
Numbers in Normal Soils and Its Consequences ; Jour. Agr. Sci., Vol. 
5, pp. 152-221, 1903. 

Buddin, W., Partial Sterilisation of Soil by Volatile and Non- 
volatile Antiseptics; Jour. Agr. Sci., Vol. 6, pp. 417-451, 1914. 



SOIL ORGANISMS 415 

229. Nitrification. — Some agricultural plants can utilize 
ammonium salts as a source of nitrogen.^ This has been .shown 
to be true for rice, maize, peas, barley, and potatoes (see par. 
248). Most plants, however, except for rice, show a decided 
preference for nitrogen in the nitrate form. Whether these 
common crops can thrive as well on ammonium salts as on 
nitrates has not been definitely demonstrated. In most arable 
soils the transformation of nitrogen does not stop with its 
conversion into ammonia, but goes on by an oxidation proc- 
ess to the formation of nitrous acid. The nitrous acid, after 
reaction with a base, is farther oxidized, a salt of nitric acid 
resulting. This process of oxidation is generally spoken of 
as nitrification. The reactions involved may be written as 
follows : 

2NH3 + 30., = 2HNO2 + 2HoO 2 

2HN0., + CaH^CCOg);, = CaCNO^s + SH^O + 2C0o ^ 

Ca(Nd2)2 + Oo = Ca(N03)o 

Each of these steps is brought about by a distinct bacteri- 
um, but the groups are closely related. Collectively they are 
called nitrobacteria. Nitrosomonas and Nitrosococcus are 
the bacteria concerned in the conversion of ammonia into 
nitrous acid or nitrites. The former are supposed to be char- 
acteristic of European, and the latter of American, soils. 
The organisms concerned in the oxidation of nitrites to ni- 

^Kelley, W. P., The Assimilation of Nitrogen by Bice; Haw. Agr. 
Exp. Sta., Bui. 24, 1911. 

Hutchinson, H. B., and Miller, N. H. J., The Direct Assimilation of 
Inorganic and Organic Forms of Nitrogen by Higher Plants; Centrlb. 
f. Bakt., II, Band 30, Seite 513-547, 1911. 

^ Loew states that the reaction is as follows : 

2NH3 + 2O2 = 2HN0., + 4H 

Loew, O., Die Chemischen V erJuiltnisse des BaJcterienlebens: II. 
Centrlb. f. Bakt., II, Bd. 9, Seite 690-697, 1891. 

^ It has often been suggested tliat the acid produced by the nitrifying 
process is of considerable importance in rendering mineral nutrients 
available. While this may be true, the extent to which the solution 
phenomenon takes place and its practical significance have never been 
satisfactorily established by experimentation. 



416 NATURE AND PROPERTIES OF SOILS 

trates are generally designated as Nitrobacter. In practice 
these bacteria are generally spoken of as nitrite and nitrate 
organisms.^ The conditions favoring the two groups are 
practically the same. As a consequence, nitrification is gen- 
erally discussed as though the transformation was only one 
step and depended on one group of organisms.^ 

Just as ammonification follows closely on putrefaction, so 
nitrification closely accompanies the production of ammonia. 
In fact, the processes are so well synchronized in a normal 
soil that only traces of ammonia and nitrites are usually 
found. The nitrates, however, may accumulate in large 
amounts. 

Marked differences have been noted in the nitrifjdng ^ 

* While it was known from the middle of the nineteenth century that 
nitrogenous compounds added to the soil quickly produced nitrates, it 
was not until 1878 that Schloessing and Muntz demonstrated that the 
process was biological. In 1890 Winogradsky succeeded in isolating 
the organisms. As they do not develop on ordinary medium, as do 
the decay and ammonifying bacteria, a special technique was necessary. 
Winogradsky used silicic-acid-gel plates containing certain inorganic 
salts, as he found that the presence of even small amounts of organic 
matter prevented the development of the organisms. In the soil, how- 
ever, well-decayed organic matter generally stimulates rather than de- 
presses nitrification. For a review of literature and methods of isol^at- 
ing nitrifying organisms, see Gibbs, W. M., The Isolation and Study of 
Nitrifying Bacteria; Soil Sci., Vol. VIII, No. 6, pp. 427-471, 1919. 

^ Kaserer has isolated an organism, which he called B. Nitrator, that 
can oxidize ammonia directly to nitrate. He writes the reaction as 
follows : 

NH3 + H2CO3 + O, = HNO3 + H,0 + CH,a 

He thinks that the energy necessary for the completion of the reac- 
tion is obtained from the formaldehyde (CHjO) as follows: 
CH2O + O2 = H2O + CO2 + Energy 

The correlation between carbon dioxide production and nitrate accumu- 
lation lends probability to this theory. 

Kaserer, H., On Soine New Nitrogen Bacteria with Autotrophic Habits 
of Life; Noted in Exp. Sta. Record, Vol. 18, p. 534, 1905-1906. 

' The nitrifying efficiency of a soil is usually determined by treating 
a 100-gram sample held in a tumbler with a suitable amount of ammonia 
sulfate or some other readily nitrifiable material. After incubation for 
a suitable period at optimum temperature and moisture, the increase of 
nitrate nitrogen is determined. This method is merely comparative and 
measures only the nitrate accumulation. Its value is limited as it does 
not simulate field conditions. 



SOIL ORGANISMS 



417 



power of different soils. Highly productive soils have gen- 
erally been found to maintain a greater nitrifying efficiency 
than less productive soils, but this is not always the case, 
as factors other than available nitrogen may limit the pro- 
ductiveness of a soil. 

With the formation of nitrate nitrogen, the main portion 
of the nitrogen cycle is completed, since plants absorb most 
of their nitrogen as the nitrate ion. Of this cycle, from 



ANIMAL- 




SYNTHESIS 

COMPLEX '^^ / 

COMPOUNDS ^^v^ / 



REDUCTION 

FREE N 




GREEN FARM 
MANURE 

DECAY 

- PARTIALLY DECAYED 
C0MP0UNJi:)3 

1 

.ANMONIFICATION 
^---- AMMONIA 



NITRIFICATION 

NITRATES -^NITRITES 




Fig. 59. — Diagram representing the movements of nitrogen between 
soil, plants, animals and the atmosphere. These transformations 
are termed the "nitrogen cycle." 



plant to soil, and from soil to plant again, the nitrification re- 
action is the weakest point, since the other biological changes 
proceed to a certain extent in spite of unfavorable soil con- 
ditions. Nitrification is easily retarded and may even be 
brought to a standstill. As a consequence, the factors affect- 
ing this particular portion of the nitrogen cycle are of special 
interest. A soil favorable to nitrification is generally wholly 
favorable to the other desirable processes involving nitrogen 
transformations. 



418 NATURE AND PROPERTIES OF SOILS 

230. Relation of soil conditions to nitrification. — Al- 
though a very great number of factors influence the process 
of nitrification, the principal controls may be listed as fol- 
lows: (1) presence of nitrifiable substance, (2) aeration, (3) 
temperature, (4) moisture, (5) soil reaction, and (6) the 
presence of soluble salts, 

A peculiarity in the artificial cultivation of nitrifying bac- 
teria is that they cannot be grown in artificial media con- 
taining organic matter. In the soil, however, organic matter, 
when well decayed, stimulates nitrification,^ provided aera- 
tion and other conditions are favorable (see par. 313). The 
application of twenty tons of farm manure to the acre to sod 
on a clay loam soil for three consecutive years, at Cornell 
University,^ resulted in a larger accumulation and probably 
a larger production of nitrates on the manured soils than 
on a contiguous plat of similar soil left unmanured. This 
was especially true during the third year of the application, 
when the land was in sod, and also during the fourth year, 
when no manure was applied to either plat and when both 
plats were planted to maize, as may be seen from Table XC 
(page 419). 

These data indicate not only a marked influence of organic 
matter on nitrification but also an effect from aeration. Even 
allowing for a direct and differential influence on nitrifica- 
-tion by the two crops, it is evident that tillage is a factor. 
Further experimental data from Cornell University may be 
quoted. Columns of soil eight inches in diameter and eight 
inches in depth were removed from a field of clay loam on 
the Cornell University farm and carried to the greenhouse 
without disturbing the original structure of the soil. At 
the same time, vessels of similar size were filled with soil dug 
from a spot near by. These may be termed unaerated and 

^ The turning under of a green-manuring crop generally depresses 
nitrification at first. Once the decay process is well under way, nitrifica- 
tion activities seem to be stimulated. 

^ Unpublished data. Cornell Agr. Exp. Sta., Ithaca, N. Y. 



SOIL ORGANISMS 



419 



Table XC 

nitrate accumulation on heavily manured and on un- 
manured soil. 





NO3 IN Parts to a Million of 
Dry Soil 


Crop 


Unmanured 
Soil 


Twenty Tons 

Manure to the 

Acre for Three 

Years 


Timothy (3rd year) 

April 23rd 

June 13th 

August 14th 


8.2 

.8 

1.8 

17.5 

50.0 

151.0 


21.0 
1.1 
3.0 


Maize following timothy 

May 19th 

July 6th 

August 10th 


20.1 
105.0 
184.0 







aerated soils. Both were kept at the same temperature and 
moisture content in the greenhouse, but no plants were grown 
on them. The accumulation of nitrates was as follows: 



Table XCI 



Time of Analysis 


Nitrates, Parts per Million Dry 
Soil 




Unaerated Soil 


Aerated Soil 


When taken from field .... 
After standing one month. . 
After standing two months. 


3.2 
4.2 
9.0 


3.2 
17.6 
45.6 



It has often been assumed that carbon dioxide is a detri- 
mental factor in biological activity in two respects: by the 
replacement of oxygen and by a toxic influence on the organ- 



420 NATURE AND PROPERTIES OF SOILS 

isms. Recent experimentation/ however, indicates that car- 
bon dioxide has little or no effect on nitrification and am- 
monification as long as appreciable quantities of oxygen are 
present. Aeration, insofar as most biological activities are 
concerned, has to do more with the presence of oxygen than 
the elimination of the carbon dioxide which is always form- 
ing. 

Since aeration is such a factor in nitrification, the trans- 
formation is very largely confined to the surface layers of 
soil, except in the rich and porous subsoils of arid and semi- 
arid regions. The lack of nitrate formation in the lower 
depths is probably influenced by temperature as well as by 
lack of oxygen and organic matter. At 5° C. nitrification is 
very feeble. The optimum temperature seems to range from 
25° to 30° C. The drainage of a soil probably promotes nitri- 
fication quite as much by facilitating a rise of temperature 
as by promoting the entrance of oxygen, especially in the 
spring. 

The speed with which nitrification proceeds in a soil is 
governed to a marked extent by water content,^ the process 
being retarded by both low and high moisture conditions. 
In practice, it is safe to assume that the optimum moisture 
as recognized for higher plants is optimum for nitrification 

^ Plummer, J. K., Sovie Effects of Oxygen and Carbon Dioxide on 
Nitrification and Ammonification in Soils; Cornell Agr. Exp. Sta., Bui. 
384, 1916. 

^Coleman, L. C, TJntersuchungen iiber Nitrifikation ; Centbl. f. Bakt., 
II, Bd. 20, Seite 401-420 and 484-513, 1908. 

Fraps, G. S., The Production of Active Nitrogen in the Soil; Tex. Agr. 
Exp. Sta., Bui. 106, 1908. 

Patterson, J. W., and Scott, P. E., The Influence of Soil Moisture 
upon Nitrification; Jour. Dept. Agr., Victoria, Vol. 10, pp. 275-282, 
1912. 

Stewart, E., and Greaves, J. E., The Production and Movement of 
Nitric Nitrogen in Soil; Centbl. f. Bakt., II, Bd. 34, Seite 115-147, 
1912. 

Gainey, P. L., The Effect of Time and Depth of Cultivating ai 
Wheat Seed-bed Upon Bacterial Activity in the Soil; Soil Sci., Vol. 
II, No. 2, pp. 193-204, 1916. 



SOIL ORGANISMS 421 

also. Greaves and Carter ^ found that a moisture content of 
about 55 per cent, of the water-holding capacity, as determined 
by the Hilgard method (see par. 90), was especially favorable 
for nitrification. 

It has generally been considered that nitrification was very 
much retarded if not actually brought to a standstill in an 
acid soil." Recent data,^ however, seem to indicate that the 
process will proceed in acid soil, although the addition of 
lime in some form is usually l)eneficial. The marked stimula- 
tion of liming to certain crops may be due partially to the in- 
fluence of the lime on the nitrifying organisms. This rela- 
tionship should be particularly noticeable if the crop in 
question is unable to utilize organic or ammoniacal forms of 
nitrogen. 

The influence of certain mineral salts is quite significant.* 
Small amounts of salts, even those of manganese, stimulate 
the process. Sodium nitrate, unless applied in excessive 
amounts, promotes the nitrification of dried blood and cotton- 
seed meal. In general, the stimulation of soil bacteria by the 
application of fertilizer salts is coordinate with the stimula- 
tion ordinarily observed in higher plants. Rational fertilizer 
practice, therefore, promotes nitrification, and no important 
retarding influences may be expected on bacterial activity 
unless the crop is itself directly injured. 

^ Greaves, J. E., and Carter, E. Gr., Influence of Moisture on the 
Bacterial Activities of the Soil; Soil Sci., Vol. X, No. 5, pp. 361-387, 
1920. 

"Hall, A. D., Fertilizers and Manure, pp. 62-64, New York, 1909. 

^ Temple, J. C, Nitrification in Acid or Non-basic Soils; Ga. Agr. 
Exp. Sta., Bui. 103, 1914. 

White, G. W., Nitrification in Belation to the Beaction of the Soil; 
Penn. Agr. Exp. Sta., Ann. Eep. 1913-14, pp. 70-84, 1916. 

* Kelley, W. P., Nitrification in Semiarid Soils; Jour. Agr. Ees., 
Vol. VII, No. 10, pp. 417-437, 1916. 

Brown, P. E., and Hitchcock, E. B., The Effect of Alkali Salts on 
Nitrification; Soil Sci., Vol. IV, No. 5, pp. 207-229, 1917. 

Brown, P. E., and Minges, G. A., The Effect of Some Manganese 
Salts on Ammonification and Nitrification; Soil Sci., Vol. II, No. 1, 
pp. 67-85, 1916. 



422 NATURE AND PROPERTIES OF SOILS 

231. Influences of higher plants on nitrification. — It has 

been known for some time that the nitrate content of a soil 
varies with The crop that occupies the land. King and AVhit- 
son ^ reported in 1901 that the accumulation of nitrates was 
greatest under maize, with potatoes next and alfalfa and 
clover much lower. Stewart and Greaves,^ in an experiment 
covering several years, also found that maize allowed the great- 
est accumulation, with potatoes, oats, and alfalfa following 
in the order named. Brown and Maclntire ^ report forty 
times more nitrates in a soil cropped to maize than when 
planted to grass. As the moisture content was practically 
the same in each case, the difference cannot be ascribed to 
this influence. 

Perhaps the most extensive work along this line is that of 
Lyon and Bizzell.* They noted a characteristic relationship 
between the crop at different stages of growth and the cor- 
responding nitrate content of the soil. During the most ac- 
tive growing period of maize, although the crop was absorb- 
ing nitrogen in large amounts, the nitrates were frequently 
higher under the maize than in a contiguous fallow plat. Oat 
land contained less nitrates, while grass seemed to retard 
markedly the accumulation of nitrates. Whether the nitrate 
organisms are stimulated by certain plants or whether nitrate 
formation is merely depressed more by some plants than by 
others is not known. It is clear, however, that the relation- 
ship of crop to nitrification must be reckoned with in practical 

^ King, F. H., and Whitson, A. E., Development and Distribution of 
Nitrates and Other Soluble Salts in Cultivated Soils; Wis. Agr. Exp. 
Sta., Bui. 85, 1901. 

^ Stewart, E., and Greaves, J. E., Tlie Production and Movement of 
Nitric Nitrogen in Soil; Centbl. f. Bakt., II, Band 34, S. 115-147, 
1912. 

^ Brown, B. E., and Maclntire, W. H., Seasonal Nitrification, Soil 
Moisture and Lime Requirement in Four Plats Receiving Sulfate of 
Ammonia; Penn. Agr. Exp. Sta., Eep. 1909-1910, pp. 57-63. 

''Lyon, T. L., and Bizzell, .1. A., Some Relations of Certain Higher 
Plants to the Formation of Nitrates in Soils; Cornell Agr. Exp. Sta., 
Memoir 1, 1913. 



SOIL ORGANISMS 



423 



soil management as well as the effect of nitrification on plant 
growth. 

The influence of plants on nitrification is not confined to 
the period in which they are growing on the soil. Lyon and 
Bizzell, in the investigation previously mentioned, found that 
certain plants grew better when preceded by one species 
rather tlian by another. These authors, as already explained, 
have suggested that certain higher plants directly influence 
nitrification with varying intensity. The question now arises 
as to the possibility of such plants influencing the process of 
nitrate formation after their removal. 

The following data from Lyon and Bizzell suggest that, 
while the effect is variable, plants seem definitely to influence 
the production of nitrates during the season after they have 
been removed. All of the plats were kept bare in 1911. 



Table XCII 





Season 1910 


Nitrates in Soil Kept 
Bare in 1911 
Parts Per Million 


Treatment 
IN 1910 


Nitrates in 

Soil, Parts 

per Million, 

Seasonal 

Average 


Nitrogen 

IN Crop, 

Pounds Per 

Acre 


May 1 


June 28 


Maize 


167 
136 

104 

108 

90 
126 


3 
43 

29 


52 
50 

28 
43 

22 
36 


37 


Bare 


35 


Potatoes 

Bare 


26 
32 


Oats 


22 


Bare 


33 







These results indicate that maize exerts a stimulating influ- 
ence during the following summer. Oats and potatoes seem 
to depress nitrate accumulation. 

232. Relation of nitrification to soil fertility. — In spite 
of the immense amount of work that has been done on the bio- 



424 NATURE AND PROPERTIES OF SOILS 

logical problems of the soil, no definite relationships have 
been established between any given transformation and the 
productivity of the soil. General correlations have been re- 
peatedly observed ^ but specific relationships, when recorded, 
are difficult to ascribe to other than chance concordance. Of 
all of the biological transformations, nitrification seems most 
likely to correlate with productivity, since most plants use 
large amounts of nitrate nitrogen. 

Available data seem to show that there is a general correla- 
tion between the nitrifying capacity of soils and their crop- 
producing power.^ Such a statement, however, does not imply 
that the productivity of soils, insofar as nitrogen is a limiting 
factor, is especially controlled by nitrification. Arable soils 
usually contain abundant nitrifying organisms, which seem 
to oxidize ammonia to the nitrate form as fast as it is pro- 
duced. It would appear that nitrification is only one of the 
many factors that govern productivity, a high nitrate content 
of a soil accompanying, rather than controlling, high crop 
production. 

233. Reduction of nitrates and allied compounds. — Ni- 
trates may be removed from the soil in three ways: (1) by 
drainage, (2) by plant absorption, and (3) by reduction to 
free nitrogen. The loss of nitrogen by leaching and by crop- 
ping has already been adequately treated. It has been shown, 
for example (see par. 163), that as high a loss as 77 pounds of 
nitrogen to the acre a year may be expected from a heavy 

^ Ashby, S. F., The Comparative Nitrifying Power of Soils; Jour. 
Chem. Soc, London, Vol. 85, pp. 1158-1170, 1904. 

Russell, E. J., and Hutchinson, H. B., The Effect of Partial Sterili- 
sation of Soils on the Production of Plant Food; Jour. Agr. Sci., Vol. 
Ill, pp. 111-144, 1909. 

Kellerman, K. F., and Allen, E. R., Bacteriological Studies of the 
Trucl-ee-Carson, Irrigation Project; U. S. Dept. Agr., Bur. Plant Ind., 
Bui. 211, 1911. 

Brown, P. E., Relation Between Certain Bacterial Activities in Soils 
and Their Crop Producing Power; Jour. Agr. Res., Vol. V, pp. 855- 
869, 1916. 

* Gainey, P. L., The Significance of Nitrification as a Factor in SoU 
Fertility; Soil Sci., Vol. Ill, No. 5, pp. 399-416, 1917. 



SOIL ORGANISMS 425 

soil through the combined influence of cropping and drainage. 
This is equivalent to a removal of about 520 pounds of sodium 
nitrate as far as the nitrogen contained is concerned. 

While the removal of nitrogen from the soil is due very 
largely to the phenomena just referred to, the loss of nitro- 
gen through reduction demands a certain amount of atten- 
tion. Reduction includes the change of nitrates to nitrites, 
to ammonia and even to free nitrogen.^ In the same way 
nitrites may be reduced to ammonia and the latter to ele- 
mental nitrogen. When the proeess is carried to completion 
there is opportunity for an escape of some nitrogen to the at- 
mospheric air. The loss of nitrogen is not the important con- 
sideration, however. The interference with plant nutrition, 
which naturally occurs, is much more serious and justifies 
the attention which the phenomena have received from bac- 
teriologists. 

The number of organisms that are capable of accomplishing 
one or more of the reduction processes is very large. This is 
due to the facultative character of the soil flora, which is 
able to alter its functions to suit the conditions. Thus B. 
mycoides, which is a normal decay and ammonifying organ- 
ism, may, under anaerobic conditions become a vigorous re- 
ducing agent. Other specific reducing organisms are : — B 
ramosus and B. pestifer, B. subtilis, B. mesenterious vul- 
gatus, B. denitrificans, and many others. It is probable that 
fungi also are able to effect the transformation. 

Most of the reducing bacteria perform their functions only 
in presence of a limited amount of oxygen, while others can 
operate in the presence of a more liberal supply. In general, 
thorough aeration of the soil impedes the process to a consid- 
erable degree. Straw apparently carries an abundant supply 
of such organisms, and it is consequently possible to reach a 

^The reaction may be illustrated empirically as follows: 
2HNO3 = 2HNO2 + Oj. 
4HNO2 z= 2H.0 + 2N, + 3O2. 
HNO3 + H..0 = NH3 + 20.,. 



426 NATURE AND PROPERTIES OF SOILS 

point in manuring at which reduction takes place. When 
fifty tons or more of farm manure, in addition to a nitrate 
fertilizer, are added to the soil, unfavorable reactions may 
occur. Plowing under heavy crops of green-manure may 
produce the same result. In either case the best way to over- 
come the difficulty is to allow the organic matter partly to de- 
compose before adding the fertilizer. The removal of the 
easily decomposable carbohydrates needed by the reducing 
organisms decreases or precludes their activity in this 
direction. 

Under ordinary farm conditions conversion to free nitrogen 
is of no significance in the soil where proper drainage and 
good tillage are practiced. Warington ^ showed that if an 
arable soil is kept saturated with water to the exclusion of air, 
nitrates added to the soil are decomposed, with the evolution 
of nitrogen gas. As lack of drainage is usually most pro- 
nounced in early spring, when the soil is likely to be depleted 
of nitrates, it is not likely that much loss occurs in this way 
unless a nitrate fertilizer has been added. Among the many 
difficulties arising from poor drainage the reduction of an 
expensive fertilizer may be no inconsiderable item. 

234. Assimilation of nitrates and allied compounds. ^ — 
In addition to the nitrate-reducing organisms already men- 
tioned, there are other bacteria and fungi that utilize nitrates, 
nitrites, and ammonia. Like higher plants, they convert 
the nitrogen into organic nitrogenous substances. The proc- 
ess is therefore, one of synthesis, rather than of reduction al- 
though reduction often occurs at the beginning of the proc- 
ess. As such organisms operate in the dark, they must have 
organic acids or carbohydrates as a source of energy. This 
means of nitrate disappearance is probably of much more 

^Warington, K., Investigations at BotJmmsted Experimental Station; 
U. S. Dep.t. Agr , Office of Exp. Sta., Bui. 8, p. 64, 1892. 

^ The term denitrifieation is often used in referring to the reduction 
and assimilation of nitrates and allied compounds in the soil. The word 
is so loosely used in soil literature that it has seemed best to ignore it, 
at least for the present. 



SOIL ORGANISMS 



427 



practical importance than nitrate reduction, yet even less is 
known regarding the phenonuMia. Many tlifferent forms of 
bacteria and fungi are probably capable of assimilating 
nitrogen, but what conditions favor their activity in this re- 
spect cannot be stated definitely/ To make the problem more 
intricate higher plants seem to be a factor to a certain ex- 
tent in this type of nitrate disappearance. Seasonal influ- 
ences also have been noted, which suggest the possibility of a 
special nitrate assimilating flora. 

Nitrate accumulation always proceeds slowly on sod land, 
especially if the soil is heavy. Lack of sufficient moisture or 
unfavorable temperature relations do not always adequately 
account for this phenomenon. An experiment at Cornell Uni- 
versity - is typical of the conditions mentioned above. In this 
case, maize and grass were grown side by side, the nitrates 
being determined at frequent intervals during the season. 
The nitrates are expressed in parts per million of dry soil for 
the various months. 

Table XCIII 

nitrates in parts per million under maize and sod. 
cornell university. 



Month 



April . . 
May . . . 
June. . 
July . . 

August 



Nitrates, Parts per Million Dry 
Soil 




17.1 

40.3 

194.0 

186.7 



' Murray has found at the Washington Agricultural Experiment Sta- 
tion that the addition of straw to the soil markedly aided the bacterial 
utilization of nitrates. The numbers of bacteria increased without 
reference to the groups present. 

Murray, T. J., The Effect of Straw on the Biological Soil Processes; 
Soil Sci., Vol. XII, No. 3, pp. 2.33-259, 1921. 

* Unpublished data. Cornell Agr. Exp. Sta., Ithaca, N. Y. 



428 NATURE AND PROPERTIES OF SOILS 

The high nitrate accumulation under the maize is probably 
due to the tillage and aeration which the soil received and 
possibly to the direct stimulation of the crop on nitrification. 
The low amounts of nitrate nitrogen in the grass land are 
probably due, at least partially, to the influence of the sod in 
encouraging nitrate assimilation by the soil organisms. The 
nitrifying power of the sod soil is probably much greater 
than the data just presented would lead one to suspect. Sodi- 
um nitrate applied to grass at Cornell University was found 
to be changed to other than the nitrate form very rapidly, 
even when the amounts added were extremely large. This 
rapid disappearance of the nitrate form of nitrogen is not 
readily accounted for by cropping and drainage removal. 
Such facts lend considerable plausibility to the suggestions 
made above, regarding the encouragement which the synthetic 
removal, especially of nitrates, receives from organisms when 
the soil is under a grass crop. 

The synthetic removal of nitrates, nitrites, and ammonia 
assumes considerable importance at certain times of the year. 
It seems to be a natural means of conserving an important 
soil constituent, since nitrate nitrogen is extremely soluble 
and easily lost by drainage. The nitrogen thus affected is 
changed to a more or less stable form, from which nitrates 
may be produced during the following year. The use of a 
cover-crop in an orchard during the late summer and fall is 
often practiced. A disappearance of nitrates but not a loss of 
nitrogen thus occurs and the trees are early forced into the 
resting stage. 

235. Natural acquisition of nitrogen by the soil. — Since 
all of the nitrogen now found in the soil was probably ac- 
quired from the atmosphere, the natural forces which facili- 
tate such a transfer assume considerable practical importance. 
The more rapid the natural acquisition of nitrogen from the 
air, the less serious will be the nitrogen problem in agricul- 
tural practice. 



SOIL ORGANISMS 



429 



Three modes of nitrogen fixation are usually recognized: (1) 
rain-water additions, (2) the action of soil organisms func- 
tioning independently of living higher plants, and (3) the 
influence of organisms functioning parasitically or symbi- 
otically in the soil. 

236. Additions of nitrogen in rainwater. — Nitrogen oc- 
curring in rainwater is generally in the nitrate and ammoni- 
cal forms and, consequently, is readily available to plants. 
The amounts thus brought down are quite variable, usually 
fluctuating markedly with season and location. The follow- 
ing table gives some of the more important findings regarding 
the amount of nitrogen thus added to the soil in various parts 
of the world. 

Table XCIV 





Years 

OF 

Record 


Rainfall 

IN 

Inches 


Pounds to the 
Acre a Year 


Location 


Ammo- 

niacal 

Nitrogen 


Nitrate 
Nitrogen 


Harpenden, England ^ . . . . 

Garford, England - 

Flahult, Sweden ^ 


28 
3 
1 

2 

10 

6 


28.8 
26.9 
32.5 
27.6 


2.64 
6.43 
3.32 
4.54 

4.02 

4.42 

11.50 


1.33 
1.93 
1.30 


Groningen, Holland * 

Bloemfontein and Durban, 
S Africa "^ 


1.46 
1.39 


Ottawa, Canada ^ 


23.4 
29.3 


2.16 


Ithaca, New York ^ 


1.01 



^Russell, E. J., and Richards, E. H., The Amount and Composition 
of Bain Falling at Bothamsted ; Jour. Agr. Sci., Vol. IX, pp. 309-337, 
1919. 

^Crowther, C, and Ruston, A. G., The Nature, Distribution and 
Effects upon Vegetation of Atmospheric Impurities In and Near an 
Industrial Town; Jour. Agr. Sci., Vol. IV, pp. 25-55, 1911. 

'Von Feilitzen, H., and Lugner, I., On the Quantity of Ammonia 
and Nitric Acid in Bainwater Collected Near Flahtdt, in Sweden; Jour. 
Agr. Sci., Vol. Ill, pp. 311-313, 1910. 

"•Hudig, J., The Amounts of Nitrogen as Ammonia and Nitric Add 



430 NATURE AND PROPERTIES OF SOILS 

Apparently the ammoniacal nitrogen is always consider- 
ably larger in amount than that in the nitrate form. It is 
also noticeable that while the nitrate nitrogen is about the 
same for every station, the nitrogen in the form of ammonia 
shows wide variations. The quantities at Ithaca, New York, 
are considerably larger than those from any other station. 
Considering the figures as a whole, it seems fair to assume 
that on the average about 4i/> pounds of ammoniacal and II/2 
pounds of nitrate nitrogen fall on every acre of soil yearly 
in rainwater. Assuming that all of this nitrogen passes into 
the soil, an average gain to the acre of 6 pounds of nitrogen 
may be expected. 

It is interesting at this point to compare such a gain with 
the annual loss of nitrogen from the soil. The removal of 
nitrogen from the Cornell lysimeter soils (see par. 163), 
through drainage and cropping combined, amounted to 69.0, 
77.8 and 56.9 pounds yearly to the acre, respectively, for a 
bare soil, one carrying a standard rotation, and one continu- 
ously in grass. While a gain of 6 pounds to the acre yearly 
seems rather insignificant in comparison to these figures, such 
an addition is of considerable importance over a period of 
years, and has had much to do with the accumulation of the 
nitrogen of our arable soils. Such a gain is equivalent in a 
practical way to the addition of about 40 pounds of commer- 
cial sodium nitrate to the acre yearly. 

237. Acquisition of nitrogen by free-fixing organisms. — 
While it has long been known that the soil contains a great 
variety of organisms, it is only in recent years that it has been 

in the Rainwater Collected at Uithuiser-Meeden, Gronigen; Jour. Agr. 
Sci., Vol. IV, pp. 260-269, 1912. 

^ Juritz, C. F., Chemical Composition of Bain in the Union of South 
Africa; S. Africa Jour. Sci., Vol. 10, pp. 170-193, 1914. 

'Shutt, F. T., and Dorrance, E., The Nitrogen Compounds of Bain 
and Snow ; Proc. and Trans. Boy. Soc. Canada, Vol. XI, No. 3, pp. 63-71, 
1917. 

'Wilson, B. D., Nitrogen in the Rainwater at Ithaca, New York; 
Soil Sci., Vol. XI, No. 2, pp. 101-110, 1921. 



SOIL ORGANISMS 431 

definitely shown that certain of these organisms have the 
power of utilizing atmospheric nitrogen, which later becomes 
a part of the nitrogenous matter of the soil. Boussingault ^ 
in 1858 suggested the possibility of such a phenomenon, but 
it was not until 1883 that Berthelot ^ began experiments by 
which he demonstrated that bare soils appreciably increase 
in nitrogen on exposure under such conditions. Winograd- 
ski ^ in 1894 was the first, however, to isolate an organism 
capable of affecting such a transformation. This bacterium 
was an anaerobic, rod-shaped organism producing spores 
and a boat-shaped mass (Clostridium) ; hence the name, Clos- 
iridium pastorianum. It is very widely distributed in soils. 

The most important organism fixing nitrogen independently 
in the soil was discovered by Beijerinck * in 1901. This or- 
ganism was an aerobic bacillus to which he gave the name 
Azotobacter. It was at first thought that this bacillus could 
not fix nitrogen unless certain other organisms, such as Granu- 
lobacter, Radiobacter and Aerobaeter, were also present. Lip- 
man ^ has shown this idea to be erroneous, although the effi- 
ciency of Azotobacter is much higher in mixed than in pure 
cultures. A number of different species of Azotobacter have 
been studied, the A. chraococcum apparently being the most 
widespread. 

Clostridium pastorianum and Azotobacter are by no means 
the only soil organisms capable of fixing nitrogen. Among 

^ See Voorhees, E. B., and Lipman, J. G., A Eeview of Investigations 
in Soil Bacteriology ; U. S. Dept. Agr., Office of Exp. Sta., Bui. 194, 
1907. 

^ Berthelot, M., Becherches nouvelles sur les microorganisms fixateurs 
de I'azote; Compt. Eend. Acad. Sci. Paris, Tome 115, pp. 569-574 and 
842-849, 1892-93. 

' Winogradsky, S., Sur I'assim-ilation de I'azote gaseux de I' atmosphere 
par les microbes; Compt. Rend. Acad. Sci. Paris, Tome 118, pp. 353-355, 
1894. 

■•Beijerinck, M. W., Vher Oligonitrophile Milroben; Centrbl. Bakt., 
II, Bd. 7, S. 561-582, 1901. 

' Lipman, J. G., Experiments on the Transformation and Fixation of 
Nitrogen by Bacteria; N. J. Agr. Exp. Sta., 24th Ann. Rep., pp. 217-285, 
1903. 



432 NATURE AND PROPERTIES OF SOILS 

bacteria, B. mesentericus, B. pneumonice, B. radiohacter, B. 
amylohacter, B. prodigiosKS, B. asterosponis, and B. lactis 
viscusus have certain capacities in this direction. Duggar 
and Davis ^ have shown that certain filamentous fungi, such 
as Phoma hetoe, Aspergillus niger, Pencillium digitatum, 
and others have the ability of utilizing atmospheric nitrogen. 
The power of fixing nitrogen is, therefore, possessed by a 
large number of different organisms, yet from the data now 
at hand the Azotobacter gi^oup seems to be of the greatest 
economic importance. The nitrogen fixed enters the nitrogen 
cycle when the organisms die, undergoing decay, ammonifica- 
tion and nitrification, thus becoming available to higher plants. 

238. Conditions for azofication and the amount of nitro- 
gen fixed.- — The term azofication relates to the fixation of 
nitrogen by the Azotobacter group,, although it may be used 
loosely in reference to all free-fixing activities. The soil con- 
ditions favorable to this phenomenon are those which are opti- 
mum for higher plants. This is especially true regarding 
aeration, temperature, and moisture relations. The process 
is encouraged by the application of lime when soils are acid 
and seem to require considerable phosphorus. This element is 
probably utilized in building up proteins within the bodies 
of the organisms. Potassium, sulfur, iron, and magnesium 
seem also to be essential to the phenomenon. The Azotobac- 
ter themselves are influenced by catalytic agents such as 
manganese. 

Since considerable energy is required for nitrogen fixation 
the presence of organic matter in the soil becomes very im- 
portant in this regard. Almost any non-toxic organic ma- 
terial may serve as a source of energy, even cellulose being 
very effective. Farm manure seems especially to encourage 

1 Duggar, B. M., and Davis, A. K., Studies in the Physiology of the 
Fungi; Ann. Mo. Bot. Garden, Vol. 33, pp. 413-437, 1916. 

^ A very excellent review of literature and discussion of Azofication : 
Greaves, J. E., Azofication; Soil Sei., Vol. VI^ No. 3, pp. 163-217, 
1918. 



SOIL ORGANISMS 433 

nitrogen fixation. The maintenance of a fair supply of soil 
organic matter is, tliercfore, as important as the regulation 
of the temperature, the oxygen, the moisture, and the reac- 
tion of the soil. While the presence of nitrates in small 
amounts seems to stimulate azofication, large quantities of 
nitric nitrogen tend to lessen nitrogen fixation. 

The amount of nitrogen fixed in the soil by organisms func- 
tioning independently of higher plants is, as might be ex- 
pected, a variable quantity. Hall ^ considers it to be on the 
average about 25 pounds yearly to the acre. Greaves - 25 
pounds, Lohnis ^ 36 pounds, and Lipman * from 15 to 40 
pounds. As a basis for calculation 25 pounds is perhaps a 
conservative and reasonable figure. A comparison of this 
figure with the 6 pounds of nitrogen brought down yearly 
in rain-water, indicates that the free-fixing organisms are 
four or five times more important than rainfall as a source of 
nitrogen, 

239. Bacillus radicicola and its relationship to the host 
plant. — It has long been recognized by farmers that certain 
crops, as clover, alfalfa, peas, beans, and some others, im- 
prove the soil, making it possible to grow larger crops of 
cereals after these plants have occupied the land. Within 
the last century the benefit has been traced to the fixation 
of nitrogen through the agency of bacteria contained in nod- 
ules on the roots. The specific plants so affecting the soil 
were found to be, with a few exceptions, those belonging to 
the family of legumes. It has furthermore been demonstrated 
that the host plant is generally able to appropriate some of 
the nitrogen so fixed and thus benefit by the relationship. 
The phenomenon was fully explained in 1886 by Hellreigel 

^ Hall, A. D., On the Accumulation of Fertility hy Land Alloiced to 
Bun Wild; Jour. Agr. Sci., Vol. I, pp. 241-249, 1905. 

=" Greaves, J. E., Azofication; Soil Sci., Vol. VI, No. 3, pp. 163-217, 
1918. 

^Lohnis, F., and Westermann, F., Vher Sticlstoff fixierende Balterien, 
IV. Centrbl. f. Bakt., II, Bd. 22, S. 234-254, 1909. 

* Lipman, J. G., Marshall's Microbiology, p. 343, 1917. 



434 NATURE AND PROPERTIES OF SOILS 

and Wilfarth. The organisms, of which there are a number 
of strains, are called Bacillus radicicola. 

The organisms living in the root nodules take free nitrogen 
from the air in the soil, and the host plant secures it in some 
form from the bacteria or their products. The presence of a 
certain species of bacteria is necessary for the formation of 
tubercles. Leguminous plants grown in cultures or in soil 
not containing the necessary bacteria do not form nodules 
and do not utilize atmospheric nitrogen, the result being that 
the crop produced is less in amount and the percentage of 
nitrogen in the crop is lower than if nodules were formed. 

The nodules are not normally a part of leguminous plants, 
but are evidently caused by an irritation of the root sur- 
face, much as a gall is caused to develop on a leaf or a branch 
of a tree by an insect. In a culture containing the proper 
bacteria the prick of a needle on the root surface will cause a 
nodule to form in the course of a few days. The entrance of 
the organism is effected through a root-hair which it pene- 
trates, and it may be seen as a filament extending the entire 
length of the hair and into the cortex cells of the root, where 
the growth of the tubercle starts. 

Even where the causative bacteria occur in cultures or in 
the soil, a leguminous plant may not secure any atmospheric 
nitrogen, or perhaps only a small quantity, if there is an 
abundant supply of readily available combined nitrogen on 
which the plant may draw. The bacteria have the ability to 
utilize combined as well as uncombined nitrogen, and prefer 
to have it in the former condition. On soils rich in nitrogen, 
legumes may, therefore, add little or no nitrogen to the soil, 
if the above ground portion of the crop is not plowed under; 
while in properly inoculated soils deficient in nitrogen an 
important gain of nitrogen may result. 

While B. radicicola is considered the organism common to 
all leguminous plants, it is now known that the organisms 
from one species of legume are not equally well adapted to 



SOIL ORGANISMS 435 

the production of tubercles on other leguminous species. Cer- 
tain cross inoculations are, however, veiy successful. The 
organisms seem to be interchangeable within the clovers, the 
vetches and the bean family. The organisms from sweet 
clover and burr clover will ino(!ulate alfalfa, while the bac- 
teria may be transferred from vetch to field pea or from cow- 
pea to velvet bean. 

It has been shown by several investigators that bacteria 
from the nodules of legumes are able to fix atmospheric nitro- 
gen even when not associated with leguminous plants. There 
would seem to be no doubt, therefore, that the fixation of 
nitrogen in the tubercles of legumes is accomplished directly 
by this organism, not by the plant itself nor through any com- 
bination of the plant and the organism. The relationship is, 
therefore, parasitical rather than strictly symbiotic, although 
the host plant benefits from the relation. The part played 
by the plant is doubtless to furnish the carbohydrates which 
are required in considerable quantities by all nitrogen-fixing 
organisms and which the legumes are able to supply in large 
amounts. The utilization of large quantities of carbohydrates 
by the nitrogen-fixing bacteria in the tubercles may also ac- 
count for the small proportion of non-nitrogenous organic 
matter in the plants. 

How the plant absorbs this nitrogen after it has been 
secured by the bacteria is not well understood nor is it known 
in exactly what form the nitrogen is at first fixed, although 
amino and amide nitrogen very soon appear.'^ Early in the 
growth of the tubercle, a mucilaginous substance is produced, 
which permeates the tissues of the plant in the form of long 
slender threads containing the bacteria. These threads de- 
velop by branching or budding, and form what have been 
called Y and T forms, known as bacteroids, which are peculiar 
to these bacteria. The threads finally disappear, and the 

^Strowd, W. H., The Forms of Nitrogen in Soybean Nodules; Soil 
Sci., Vol. XI, No. 2, pp. 123-130, 1921. 



436 NATURE AND PROPERTIES OF SOILS 

bacteria diffuse themselves more or less through the tissues of 
the root. What part the bacteroids play in the transfer of 
nitrogen is not known. It has been suggested that in this 
form the nitrogen is absorbed by the tissues of the plant. It 
seems quite likely that the nitrogen compounds produced 
within the bacterial cells are diffused through the cell-wall and 
absorbed by the plant. 

240. The practical importance of B. radicicola. — The 
nitrogen fixed by the nodule organisms may go in three di- 
rections in the soil. It may be absorbed by the host plant, 
the latter benefiting greatly by the association. This rela- 
tionship has already been discussed. Secondly, the nitrogen 
may pass in some way into the soil itself and benefit a crop 
associated with the legume. Thirdly, the nodules may decay, 
when the legume dies or is turned under, the nitrogen be- 
coming available to the succeeding crop. 

The relationship between associated legumes and non- 
legumes has been particularly studied by Lyon and Bizzell ^ 
and by Lipman.- It has been quite definitely proven that the 
non-legume may be greatly benefited by the association under 
some conditions. This accounts for the practice of growing 
timothy with clover, which has been common for centuries. 
Just how the transfer of nitrogen is facilitated yet remains 
to be shown. 

The beneficial influences of such legumes as clover, vetch, 
and alfalfa on the succeeding crops has long been taken ad- 
vantage of in practical agriculture. Until recently the stimu- 
lation has been ascribed to an actual increase of nitrogen in 
the soil, due to the growth of the legume and the activity of 
its nodule organisms. This will not always account for the 
phenomenon, since it has been shown by a number of investi- 

^ Lyon, T. L., and Bizzell, J. A., Availability of Soil Nitrogen in 
Relation to the Basicity of the Soil and to the Growth of Legumes; 
Jour. Ind. and Eng. Chem., Vol. 2, No. 7, pp. 313-315, 1910. 

^ Lipman, J. G., The Associative Growth of Legumes and Non-Legumes. 
N. .J. Agr. Exp. Sta., Bui. 253, 1912, 



SOIL ORGANISMS 437 

gators that the continuous growing of legumes, the tops being 
removed as forage, does not always increase the nitrogen con- 
tent of the soil to any greater extent than does a non-legumi- 
nous crop. 

The results of Swanson ^ are particularly striking in this 
respect. This investigator sampled a number of fields in 
Kansas that had grown alfalfa continuously for twenty or 
thirty years, at the same time obtaining soil from contiguous 
native sod. In most cases the alfalfa soil was lower in 
nitrogen than the sod. Lyon and Bizzell ^ found practically 
the same content of nitrogen in contiguous alfalfa and 
timothy soils after the crops had been growing six years. 
The maize crop following the alfalfa was nevertheless much 
greater than that after the timothy. Since the soil on which 
a legume has been growing generally has a rather high nitrify- 
ing capacity,^ the explanation seems to lie in the ready avail- 
ability of the nitrogen in the soil which bore the legume, 
rather than to the presence of an especially large amount. 

The amount of nitrogen fixed by the nodule organisms of 
a leguminous crop is very uncertain. If the soil is acid, if 
it contains alkali salts above a certain amount, or if nitrates 
develop rapidly, nitrogen fixation is markedly retarded. Much 
also depends on the virulence of the organisms, the character 
of the legume, the presence of organic matter, and other im- 
portant conditions. Hopkins * estimates that about one-third 

^Swanson, C. O., TJie Effect of Prolonged Growing of Alfalfa on 
the Nitrogen Content of the Soil; Jour. Amer. Soc. Agron., Vol. 9, 
No. 7, pp,.'^ 305-314, 1917. 

Swanson, C. O., and Latshaw, W. L., Effect of Alfalfa on the Fer- 
tility Elements of the Soil in Comimrison with Grain Crops; Soil Sci., 
Vol. VIII, No. 1, pp. 1-39, 1919. 

^Lyon, T. L., and Bizzell, J. A., Experiments Concerning the Top- 
dressing of Timothy and Alfalfa; Cornell Agr. Exp. Sta., Bui. 339, 
np. 136-139, 1913. 

^Lyon, T. L., Bizzell, J. A., and Wilson, B. D., The Formation of 
Nitrates in a Soil Following the Growth of Bed Clover and of Timothy; 
Soil Sci., Vol. IX, No. 1, pp. .53-64, 1920. 

* Hopkins, C. G., Soil Fertility and Permanent Agriculture, p. 223, 
Boston, 1910. 



438 NATURE AND PROPERTIES OF SOILS 

of the nitrogen of a normal inoculated legitme comes from 
the soil and two-thirds from the air. He also assumes that 
one-third of the nitrogen of the plant exists in the roots. Al- 
though both of these assumptions are questionable, they sug- 
gest the reason why the removal of the tops of legumes as 
forage allows no accumulation of nitrogen in the soil. 

According to Hopkins, the nitrogen in the tops of legumes 
is a rough measure in general of the nitrogen fixed. On such 
an assumption, the growth of red clover should facilitate the 
fixation of about 40 pounds of nitrogen for every ton of air- 
dry material. On the same basis, the figure should be about 
50 pounds for alfalfa, 43 pounds for cowpeas, and 53 pounds 
for soybeans. These figures, even though they are obviously 
incorrect, give some idea of the importance of B. radicicola in 
nitrogen fixation. The growth of an average leguminous 
crop under proper conditions probably is accompanied by a 
fixation of 80 to 100 pounds of nitrogen. Of the three nat- 
ural methods by which atmospheric nitrogen may be fixed 
by the soil that facilitated by the nodule organisms seems 
at first thought to be considerably the most important. It 
must be remembered, however, that with an average rotation 
a legume occupies the land but one or two years in three to 
six. Moreover, the gain of nitrogen in a fertile soil is but 
slight unless the crop is turned under as a green-manure. 
Unless so used the chief advantages of growing a legumi- 
nous crop lie in the increase of soil organic matter, the 
ready and favorable decay of the roots and stubble, and the 
opportunity of growing a high protein crop without ma- 
terially depleting the soil nitrogen. 

241. Soil inoculation for legumes. — Although the inocu- 
lation of the soil with free-fixing organisms has not proven 
of value, since such organisms are always present and suffi- 
ciently active if soil conditions are favorable, the inoculation 
with nodule bacteria is of considerable practical importance. 
Such organism may never have been present in a soil or may 



SOIL ORGANISMS 439 

have disappeared because of unfavorable conditions. If leg- 
umes, especially of certain types, are to be grown most suc- 
cessfully, the specific strains of B. radicicola for that crop 
must be present. 

Two general methods of inoculation are available: (1) the 
use of soil from fields where the particular legume in ques- 
tion is growing or has grown successfully; and (2) the utiliz- 
ation of artificial cultures of some form. Bacillus radicicola 
is found in the soil as well as in the plant nodules. As a 
matter of fact, this bacterium will live in the soil for long 
periods, even if the host plant is not grown. Whether it fixes 
nitrogen to any extent under such conditions is a question. 
At least the organism does not lose its virulence. Such soil 
may be spread on the land to be inoculated at the rate of 
300 to 500 pounds to the acre. It should be applied in the 
evening or on a cloudy day and harrowed in as soon as pos- 
sible, as the organisms are injured by direct sunlight. 

The soil carrying the organism may also be mixed after 
air-drying with the seed, the latter having been moistened with 
a dilute glue solution.^ Enough of the dry earth sticks to 
the seed to carry the organisms into the soil. The advantage 
of this method is that the bacteria are in contact with the seed 
and the plants become infected very soon after the seeds 
germinate. The main objection to the soil method of inocu- 
lation lies in the possibility of spreading plant diseases and 
undesirable weeds. 

* Dissolve ordinary furniture glue in boiling water, two handf uls of 
glue to every gallon of water used, and allow the solution to cool. Put 
the seed in a wash-tub, and then sprinkle enough of the solution on the 
seed to moisten but not to wet it (one quart to a bushel is sufficient), 
and stir the mixture thoroughly until all the seeds are moistened. 

Dry the inoculating soil in the shade, preferably in the barn or base- 
ment, and pulverize it thoroughly into a dust. Scatter this dust over the 
moistened seed, using from one-half to one gallon of dirt for each 
bushel of seed, mixing thoroughly until the seed no longer stick together. 
The seed is then ready to sow. 

See Vrooman, C, Grain Farming in the Corn Belt with Live Stock as 
Side Line; Farmers' Bui., No. 704, 1916. 



440 NATURE AND PROPERTIES OF SOILS 

Within recent years a number of cultures for soil inocula- 
tion have been offered to the public. The first of these util- 
ized absorbent cotton to transmit the bacteria in a dry state 
from the pure culture in the laboratory to the user of the cul- 
ture, who was to prepare therefrom another culture to be used 
for inoculating the soil. Careful investigation of this method 
showed that its weakness lay in drying the cultures on the ab- 
sorbent cotton, which frequently resulted in the death of the 
organisms. More recently liquid cultures have been placed 
on the market in this country, and these have, in the main, 
proved to be more successful, notably those sent out by the 
United States Department of Agriculture. 

Another very successful culture medium, now being used 
by the Department of Plant Physiology at Cornel University, 
is steamed soil. A soil, favorable to the development of 
nodule organisms and usually a sandy loam, is sterilized by 
steaming. It is then brought up to optimum moisture and 
later inoculated with a number of different strains of B. 
radicicola. After incubation for several days at a favorable 
temperature, the soil cultures are ready for distribution. The 
soil is sent out in small air-tight cans by parcel post. The 
advantage of such a culture is that the organisms are viru- 
lent and there is no danger from plant diseases or undesir- 
able weeds. 

When a culture of this sort is received it may be used in a 
number of different ways. It may be mixed with field soil 
at the rate of 1 pound to 300 of the latter. This 300 pounds 
of inoculated soil may then be spread on a acre of land in 
the usual way. The culture may also be disposed of by the 
glue method or it may be suspended in water and the extract 
sprinkled on the seed and dried in the shade. In either case, 
the seed should be sown as soon as possible. 

242. Resume. — The biological phases of the soil are so nu- 
merous and far-reaching that it is obviously impossible in 
summarizing their practical relationships to do more than call 



SOIL ORGANISMS 441 

attention to certain significant facts. In the first place, the 
soil fauna and flora, especially the latter, are exceedingly 
complex. Tlie number of plant forms are so numerous that 
tlie discussion already presented serves as little more than an 
introduction. In the second place, the transformations facili- 
tated by soil organisms involve all of the normal constituents 
of the soil, both organic and inorganic. Moreover, biological 
activities determine to a large degree the efficacy of every 
addition, natural or artificial, made to the land. While the 
cycles generally recognized are apparently clear cut, the 
transformations themselves are actually involved in intrica- 
cies, which man will probably never entirely unravel. 

A third pliase of outstanding importance is the relationship 
of the biological activities of the soil to the nitrogen prob- 
lem. Not only are the complex nitrogenous compounds of the 
soil readily made available to higher plants by soil organisms, 
but means are provided whereby considerable nitrogen, in- 
ert as it is, may be wrested from the atmosphere and forced 
into activity within the soil. It is not impossible that in cer- 
tain favored cases 150 pounds of nitrogen to the acre may 
be yearly added to the soil by such processes. This phase 
alone is worthy of the most careful practical study. Obvi- 
ously no_system of soil management can be wholly successful 
unless full advantage is taken of this and other biological 
possibilities of the land. 



CHAPTER XXII 
COMMERCIAL FERTILIZER MATERIALS^ 

While the use of animal excrement on cultivated soils was 
practiced as far back as systematic agriculture can definitely 
be traced, the earliest record of the use of mineral salts for in- 
creasing the yield of crops was published in 1669 by Sir 
Kenelm Digby.^ He says: "By the help of plain salt petre, 
diluted in water, and mingled with some other fit earthly 
substance, that may familiarize it a little with the corn into 
which I endeavored to introduce it, I have made the barrenest 
ground far outgo the richest in giving a prodigiously plentiful 
harvest." His dissertation does not however, show any true 
conception of the reason for the increase in the crop through 
the use of this fertilizer. In fact, the lack of any real knowl- 
edge at that time of the composition of the plant would have 
made this impossible. 

In 1804, de Saussure,^ a Frenchman, called attention, for 
the first time to the significance of the ash ingredients of 
plants not only showing that these mineral materials were 

^ The following general references may prove helpful : 

Hall, A. D., Fertilisers and Manure; New York, 1921. 

Halligan, J. E., Soil Fertility and Fertilisers; Easton, Pa., 1912. 

Van Slyke, L. L., Fertilizers and Crops; New York, 1912. 

Fraps, G. S., Principles of Agricultural Chemistry; Easton, Pa., 
1912. 

Collins, S, H., Chemical Fertilisers and Parasiticides; New York, 
1920. 

^ Digby, Kenelm, A Discourse Concerning the Vegetation of Plants; 
London, 1669. 

^ Saussure, Theodore de, Eecherclies Chimiques sur la Vegetation; 
Paris, 1804. 

442 



COMMERCIAL FERTILIZER MATERIALS 443 

obtained from the soil but pointing out that they were ab- 
solutely essential for plant growth. Liebig/ in Germany, at 
about the middle of the nineteenth century, emphasized still 
more strongly the importance of minerals to plants, refuting 
the theory, at that time current, tliat plants obtained all of 
their carbon from the soil organic matter. While he showed 
the importance of potash and phosphoric acid in manures, he 
failed to appreciate the value of nitrogenous materials, hold- 
ing that the soil received sufficient ammonia in rain-water. 
The true conception of the necessity of supplying nitrogen 
in some form was definitely established in an experimental 
way in 1857 by Lawes, Gilbert and Pugh - of the Rothamsted 
Experiment Station, England. The extreme care used by 
these investigators caused them to sterilize the soil with which 
they were working. They thus failed to discover the utiliza- 
tion of free atmospheric nitrogen by legumes. This phe- 
nomenon, so important in practical agriculture, was explained 
by Hellriegel and Wilforth in 1886. 

Between 1840 and 1850 Sir John Lawes placed the manu- 
facture of superphosphates on a commercial basis by treating 
bones and coprolites with sulfuric acid. At about this time 
the importation into Europe of Peruvian guano and sodium 
nitrate began. The commercial fertilizers industry, which 
has now attained such importance in practical agriculture, 
may be considered as dating from this period. 

243. Commercial fertilizers. — Although the commercial 
fertilizer industry is but little more than seventy years old, 
the sale of fertilizers in this country at the present time 
amounts to millions of dollars annually. Animal refuse and 

^Liebig, J. Justus von. Principles of Agricultural Chemistry with 
Special Beference to the Late Besearches Made in England; London, 
1855. Also, Chemistry in Its Applications to Agriculture and Physiology ; 
New York, 1856. 

* Lawes, J. B., Gilbert, J. H., and Pugh, E., On the Sources of the 
Nitrogen of Vegetation, with Special Beference to the Question Whether 
Plants Assimilate Free or Uncombined Nitrogen; Rothamsted Memoirs, 
Vol. 1, No. 1, 1862. 



444 NATURE AND PROPERTIES OF SOILS 

phosphates are exported, while sodium nitrate and potash 
salts are imported in large amounts. Fifty per cent, of the 
fertilizers sold in the United States are applied in the south 
Atlantic states within three or four hundred miles of the 
seaboard. Nearly one-half of the remainder is purchased by 
the New England and middle Atlantic states. West of the 
Mississippi River, the use of fertilizers, especially those car- 
rying phosphoric acid, is increasing rapidly. 

The primary function of a commercial fertilizer is to supply 
plant nutrients to the soil in such a form that the plant may 
be directly influenced by such an application. The secondary 
influences of fertilizers may be beneficial or detrimental. The 
exact nature of the secondary influences depends on the par- 
ticular fertilizer applied and especially on the type of soil 
and the crop management in vogue. 

Prepared fertilizers, as found on the market, are usually 
composed of a number of ingredients. Since these ingredi- 
ents are the carriers of the nutrient constituents, and since 
it is on their composition and solubility that the value of a 
fertilizer depends, a knowledge of the properties of these 
materials is not only of interest to every one who uses fer- 
tilizers but is also a valuable aid in their purchase. 

FERTILIZERS USED FOR THEIR NITROGEN 

Nitrogen is usually the most expensive constituent of ma- 
nure and is of great importance, since it is very likely to be 
deficient in soils. A commercial fertilizer may have its nitro- 
gen in the form of soluble inorganic salts or in organic com- 
bination. On the form depends to a certain extent the agri- 
cultural value of the nitrogen, as the soluble inorganic salts 
are very readily available to the plant, while the organic forms 
must pass through the various biological processes before 
the plant can use the nitrogen so contained. Only the best- 
known fertilizer carriers need receive particular attention 
here. 



COMMERCIAL FERTILIZER MATERIALS 445 

244. Dried blood and tankage.^ — Both of these fertilizers 
are packing-house products. The former is obtained by dry- 
ing the blood from the slaughtering pens. It comes on the 
market as a homogeneous blackish to dark greyish material, 
often slightly moist and with a characteristic odor. Its con- 
tent of ammonia (NHg) ranges from 10 to 16 per cent., de- 
pending on the grade of the fertilizer. It often contains 
traces of phosphoric acid (PgOg).^ 

Tankage is a mixture of various refuse materials from the 
slaughter-houses, such as blood, hair, scraps of meat, and hide 
and bone. It is generally steam-cooked and part of the gela- 
tin and fat removed. It is variable in composition, carrying 
from 5 to 10 per cent, of NH3 and from 3 to 8 per cent, of 
P2O5. The phosphoric acid is contained in the bone and is 
in the form of tricalcium phosphate [Ca3(P04)2]. Tankage 
is easily distinguished from blood meal by its heterogeneous 
character. 

When added to a soil, both blood and tankage undergo rapid 
decomposition, ammonification, and finally nitrification. Such 
fertilizers are, therefore, very effective in the late spring and 
summer. For early application, however, a material such 
as sodium nitrate is much better, since a biological transfor- 
mation is unnecessary in order that it may be immediately 
utilized by the plants. 

245. Other organic nitrogenous fertilizers. — Below will 
be found the composition of a number of other organic ma- 
terials that have been or are still used as fertilizers. Only two 
need explanation. Guano consists of the excrement and car- 
casses of sea fowls, the composition depending on the climate 
and position in which it is found. Guano from an arid region 
contains ammonia, phosphoric acid, and potash. Under 
humid conditions only the phosphoric acid remains in any 

*Fry, W. H., Identification of Commercial Fertiliser Materials; U. S. 
Dept. Agr., Bui. 97, 1914. 

^ The composition of commercial fertilizers is commonly expressed in 
terms of ammonia (NH3), phosphoric acid (P2O5), and potash (K^O). 



446 



NATURE AND PROPERTIES OF SOILS 



amount. Typical guano carries uric acid, urates, and am- 
monium salts. The phosphorus occurs as calcium, potas- 
sium, and ammonium phosphates. The potash is found in 
the chloride, sulfate and phosphate forms. While guano 
was once a very important fertilizer, the deposits are very 
nearly exhausted and but little now appears on the market. 
Process fertilizers are obtained by treating organic trade 
wastes and refuse with acid or with steam under pressure. 
Hydrolysis of the proteins occurs with the formation of pro- 
teoses, peptones, and simple amino acids. The water soluble 
nitrogen of such materials has been shown by Lathrop of the 
United States Bureau of Soils to be as readily available as 
that of dried blood or tankage. 



Table XCV 



Fertilizer 


NH3 


P2O. 


K,0 


Guano 

Process goods 


10-14 

1- 3 

10-13 

8-11 
,8^12 
10-16 
8h-10 
4- 6 
5e- 7 


6- 7 

10-12 

6- 7 

1- 2 
1-2 
1- 11/2 


2-5 


Hoof meal 




Fish scrap 




Leather meal 




Wool and hair waste 

Cottonseed meal 

Linseed meal 


2-3 
1-2 


Castor pomace 


1-11/2 



These compounds vary greatly in their values as fertilizers. 
Guano, process goods, and fish scrap when in the soil decom- 
pose rapidly and are as effective ordinarily as blood or tank- 
age. Untreated leather meal and wool and hair waste decay 
very slowly and are of little value as fertilizing materials. 

246. Utilization of nitrogenous organic compounds by 
plants. — One of the early beliefs in regard to plant nutrition 
was that organic matter as such is directly absorbed by higher 
plants. This opinion was afterwards entirely replaced by the 



COMMERCIAL FERTILIZER MATERIALS 447 

mineral theory propounded by Liebig ; and still later the dis- 
covery of the nitrifying process almost disposed completely of 
the belief that organic matter is used directly by higher 
plants. It is quite certain, however, that some organic nitrog- 
enous compounds furnished suitable material for some higher 
plants without undergoing bacterial change and producing 
a nitrate form of nitrogen. 

The following compounds have been shown by Hutchinson 
and Miller ^ to be readily assimilated by peas : acetamide, 
urea, barbituric acid, and alloxan. Formamide, glycerine, 
cyanuric acid, oxamine, peptone, and sodium aspartate were 
assimilated but less easily. Creatinine has been shown by 
Skinner - to be used directly by plants as a source of nitro- 
gen. Histidine, arginine, and creatine have also been found 
in soils and it has been demonstrated that they have a direct 
influence on wheat seedlings. 

These and numerous other investigations of this subject 
show that amine as well as amide nitrogen is assimilated by 
at least some agricultural plants, but to what extent most 
of these compounds may successfully replace the inorganic 
forms of nitrogen, such as the nitrates, has not been definitely 
established. Certain organic nitrogenous fertilizers^as, for 
example, dried blood — have a high commercial value, the 
nitrogen in this form selling for more a pound than the nitro- 
gen in any of the inorganic salts. Many crops, especially cer- 
tain vegetables, are most successfully grown only when 
supplied with organic nitrogenous material. Some ni- 
trate nitrogen is always present under natural soil condi- 
tions, so that crops are never limited to organic nitrogen 
alone ; and it may be that the latter form of nitrogen is most 
useful when it supplements the nitrate form. 

^Hutchinson, H. B., and Miller, N. H. J., The Direct Assimilation 
of Inorganic and Oraanic Forms of Nitrogen by Higher Plants; Centrlb. 
f. Bakt., II, Bantl 30, Seite 513-547, 1911. 

* Skinner, J. J., III. Effects of Creatinine on Plant Growth; U. S. 
Dept. Agr., Bur. Soils, Bui. 83, pp. 33-44, 1911. 



448 NATURE AND PROPERTIES OF SOILS 

247. Sodium nitrate (NaNO. -\-)} — Sodium nitrate is 
mined in Chile, occurring as a crude salt (caliche) in the 
semiarid regions along the coast. It is found near the sur- 
face under an over burden of varying thickness. The cal- 
iche contains, besides sodium nitrate, such salts as NaCl, 
K2SO4, Na.SO,, and MgSO^ besides traces of Na.COg, K0CO3, 
and boron. The refined salt, which is shipped to this country, 
carries from 2 to 3 per cent, of NaCl and KNO3. Its am- 
monium content is generally rated at about 18 per cent. 

The fertilizer appears on the market in clouded crystals of 
a yellowish cast, extremely soluble in water and quite de- 
liquescent. The fertilizer is generally alkaline to litmus. 
In the soil it diffuses rapidly and is immediately avail- 
able to plants. For this reason it. is extremely valuable early 
in the spring before nitrification is active. 

The long-continued use of sodium nitrate will tend to pro- 
duce an alkaline residue of sodium carbonate in the soil." 
This is due to the absorptive power of the soil for sodium and 
the ease with which the nitrate ions are lost in drainage. The 
plant, by using large amounts of nitrates, intensifies this se- 
lective absorption. 

The origin of the caliche deposits is problematical. The 
theory has been advanced that the origin is due to the de- 
composition of great deposits of seaweed on an uplifted con- 
tinental shelf. Another hypothesis would have the deposits 
originate from wind-carried guano dust. As rational a the- 
ory as any is proposed by Singewald and Miller,^ who believe 
the nitrates were leached from the Andes Mountains and 

^ Fertilizer materials are never pure salts. The plus after the formula 
indicates the presence of impurities. 

2 Hall, A. D., TJie Effect of the Long Continued Use of Sodium Nitrate 
on the Constitution of the Soil; Trans. Chem. Soc. (London), Vol. 85, 
pp. 950-971, 1904. Also, Brown, B. E., Concerning Some Effects of Long- 
Continued Use of Sodium Nitrate and Ammonium Sulfate on the Soil; 
Ann. Eep. Pa. State Coll., 1908-1909, pp. 85-104. 

^Singewald, J. N., and Miller, B. L., Genesis of the Chilean Nitrate 
Deposits; Econ. Geol., Vol. II, pp. 103-113, 1916. 



COMMERCIAL FERTILIZER MATERIALS 449 

carried by ground water to their present location. The con- 
centration of the salts is considered by these authors as due 
to surface evaporation and consequent upward capillary 
movement of the highly charged ground water. 

248. Ammonium sulfate ((NHJ.SO^ +).— This fertil- 
izer is a by-product from coke ovens and from the distilla- 
tion of coal in gas manufacture.^ About one-fifth of the 
nitrogen of the coal is thus driven off as ammonia, which is 
caught in special washing devices. The mother liquid is then 
distilled, the NH3 being driven into sulfuric acid. The prod- 
uct is later concentrated and the salt crystallized out. An- 
other and simpler process provides for a direct union of the 
gas and the acid, thus eliminating the washers. 

This fertilizer usually carries about 25 per cent, of am- 
monia. It usually has a greyish or greenish color due to 
coal-tar products. This commercial ammonium sulfate is 
very soluble in water and has a characteristic taste. When 
heated, it readily breal« up, giving off ammonia gas. It 
is very acid to litmus paper, due to the union of a weak 
base with a strong acid radical. The ammonia is very strongly 
absorbed by the soil and also is used to a greater extent by 
the plant than are the sulfate ions. It thus leaves in the 
soil an acid residue - which should be alleviated by lime if 
the soil is not already supplied with plenty of active calcium 
and magnesium. In a warm soil the ammonia is quickly 
nitrified to the nitrate form. This transformation is general- 

^ By-Product Colce and Gas Plants; The Koppers Company, Pitts- 
burgh. 

Sulfate of Ammonia. Its Source, Production and Use; The Barrett 
Company, New York. 

^ Hall, A. D., and Gimingham, C. T., The Interaction of Ammonium 
Salts and the Constitution of the Soil; Jour. Chem. Soc. (London), 
Vol. J)l, pt. 1, p. 677, 1907. 

White, J. W., The Besults of Long Continued Use of Ammonium 
Sulfate Upon a Besidual Limestone Soil of the Eagerstown Series; Ann. 
Rep. Pa. State Coll., 1912-1913, pp. .55-104. 

Ruprecht, R. W., and Morse, F. W., The Effect of Sulfate of Ammonia 
on Soil; Mass. Agr. Exp. Sta., Bui. 165, 1915. 



450 NATURE AND PROPERTIES OF SOILS 

ly so rapid as to make this fertilizer almost as quickly effec- 
tive as sodium nitrate. 

"While the nitrogen of ammonium salts is quickly changed 
to the nitrate combination in a well-drained soil, some plants 
seem to prefer ammoniacal nitrogen to the nitrate form. Kell- 
ner ^ in 1884 and later Kelley - demonstrated that rice plants 
growing on lowland soils use ammoniacal nitrogen rather 
than other forms. On upland soils, however, it is presumable 
that rice plants utilize nitrate nitrogen, which would indi- 
cate that some plants, at least, may adapt themselves to the 
use of a more abundant form of nitrogen. 

Hutchinson and Miller ^ found that peas obtained nitrogen 
from ammonium salts as readily as from sodium nitrate, but 
that wheat plants, although able to obtain nitrogen directly 
from ammonium salts, grew much better in a solution con- 
taining nitrates. One feature brought out by the numerous 
experiments with ammonium salts is the difference between 
plants of various kinds in respect to their ability to absorb 
nitrogen in this form. 

249. The artificial fixation of nitrogen.* — The vast store 
of atmospheric nitrogen, chemically uncombined and very 
inert, will furnish an inexhaustible supply for plants when it 
can with reasonable economy be combined in some manner to 
give a product that can be commercially transported and 
that will, when placed in the soil, become available without 
liberating substances toxic to plants. The importance of the 

' Kellner, 0., AgrikulturchemiscJie Studien iiber die Beislcultur ; 
Landw. Vers. Stat., Band 30, Seite 18-41, 1884. 

' Kelley, W. P., The Assimilation of Nitrogen by Bice; Haw. Agr. Exp. 
Sta., Bui. 24, pp. 5-20, 1911. 

^ Hutchinson, H. B., and Miller, N. H. J., The Direct Assimilation of 
Inorganic and Organic Forms of Nitrogen by Higher Plants; Centrlb. 
f. Bakt., II, Band 30, Seite .513-547, 1911. 

^Norton, T. H., Utilization of Atmospheric Nitrogen; U. S. Dept. of 
Comm. and Labor, Special Agents Ser., No. 52, 1912. 

Knox, J., Fixation of Atmospheric Nitrogen; New York. 

Slosson, E. E., Creative Chemistry, Chaps. II and III; New York, 
1920. 



COMMERCIAL FERTILIZER MATERIALS 451 

nitrogen supply for agriculture may be appreciated when it 
is considered that nitrates are being carried otl in the drain- 
age water of all cultivated lands at a surprisingly rapid rate. 
A Dunkirk silty clay loam at Cornell University/ carrying 
a rotation of maize, oats, wheat, and hay, lost in crop and 
drainage water in a period of ten years over 77 pounds to the 
acre of nitrogen annually. This is equivalent to 520 pounds 
of commercial sodium nitrate or to about 380 pounds of com- 
mercial ammonium sulfate. 

The exhaustion of the supply of nitrogen in most soils may 
be accomplished within one or two generations, unless a re- 
newal of the supply is brought about in some way. Natural 
processes provide for an annual accretion through the wash- 
ing-down of ammonia and nitrates by rain-water from the 
atmosphere, and through the fixation of free atmospheric 
nitrogen by bacteria. Farm practice of the present day re- 
quires the application of nitrogen in some form of manure, 
and, as the end of the commercial supply of combined nitro- 
gen is easily in sight, there is urgent need of discovering a 
new source. The world war has given great impetus to the 
study of the artificial fixation of nitrogen and a number of 
compounds thus produced are on the market or will appear 
shortl3^ 

250. Calcium cyanimid (CaCN. +).2— The manufacture 
of this fertilizer begins with calcium carbide (CaCg) which 
is produced by heating lime and coke together. 

CaO + 3C = CaC, + CO 

This impure carbide is then powdered and heated elec- 
trically in special ovens. At the proper temperature nitro- 
gen gas is passed through the carbide with the following re- 
sult : 

CaCa + N, = CaCN^ -f C 

*For complete data, see par. 163, this text. 
*Pranke, E. J., Cyanamid; Easton, Pa., 1913. 



452 NATURE AND PROPERTIES OF SOILS 

The product is a black dry crystalline powder of rather 
light weight, containing about 20 per cent, of NH3. It is very 
impure as shown by the following analysis: 

CaCN^ 45.9 C 13.1 

CaCO, 4.0 Fe.Og and AI.O3 1.9 

CaS ^. 1.7 SiO. 1.6 

CagPg 1 MgO 1 

Ca(OH)., 26.6 ILO 3 

Its odor and the presence of carbon are characteristic. It 
is intensively alkaline to litmus. In the soil it undergoes a 
number of very complex changes, urea ultimately being pro- 
duced. Toxic compounds are present as the reactions pro- 
ceed. It should, therefore, be placed in the soil some time be- 
fore the crop is seeded. The carbon seems to aid in the trans- 
formation as a catalytic agent. The urea quickly breaks 
down biologically to ammonia : 

CON A + 2H,0 = (NHJ2 CO3 

This ammonia is then oxidized to the nitrate form. 

251. Basic calcium nitrate (Ca(N03)2+).— This fertil- 
izer, like calcium cyanimid, is produced by the artificial fixa- 
tion of nitrogen. Air is passed through an electric arc of high 
temperature. Under such conditions a part of the oxygen and 
the nitrogen are forced together forming nitric oxide. This 
gas is then oxidized in suitable chambers to the peroxide, 
which is passed into water, producing nitric acid. The nitric 
oxide which also results is led back to the oxidizing chambers. 

The reactions are as follows : 

N, 4- 0, = 2N0 

2N0 + 0. = 2NO2 

3N0. + H,0 = 2HN0, -f NO 

The nitric acid is passed into lime-water, giving calcium 
nitrate. This fertilizer contains from 13 to 16 per cent, of 
ammonia and is intensely alkaline to litmus. Due to its high 



COMMERCIAL FERTILIZER MATERIALS 453 

deliquescence, it must either be treated in some way, which 
raises the cost of manufacture, or must be shipped in sealed 
casks. It is very soluble in water and is immediately available 
to plants. It leaves no harmful residue in the soil. 

252. Other methods of nitrogen fixation. — Calcium ni- 
trate, because of its cost, cannot compete either with sodium 
nitrate or ammonium sulfate and is not manufactured in this 
country. Calcium cyanamid is produced only in amounts 
sufficient to satisfy the demands of mixed fertilizer manu- 
facture. Its dry character makes it valuable in such com- 
pounding. 

At the present time a number of more efficient methods of 
artificially fixing nitrogen are known. The Haber process 
proved extremely successful in Germany, especially when 
supplemented by the Oswald method of converting ammonia 
into nitric acid. In the Haber method a mixture of nitrogen 
and hydrogen are placed under pressure and moderately 
heated in the presence of a catalyst. A good yield of ammonia 
results. 

N, + 3Ho = 2NH3 

In the Oswald method this ammonia is passed over a cata- 
lytic agent in the presence of oxygen. 

NH3 + 2O0 = HNO3 + H2O 

The advantage of producing both ammonia and nitric acid 
is obvious, as ammoniun nitrate (NH4NO3), ammonium phos- 
phate ((NH^)3P0J, and potassium nitrate (KNO.) may be 
produced at one plant. 

During the war Professor Bucher of Brown University per- 
fected a simple and inexpensive method of producing sodium 
cyanide synthetically. Producers gas, formed by passing air 
over hot coal, is forced through a heated revolving drum con- 
taining soda ash, iron, and coke. The reaction is as follows: 

NagCOa -f 4C + N, = 2NaCN + SCO 



454 NATURE AND PROPERTIES OF SOILS 

Ammonia may be produced very easily from the sodium 
cyanide and used as such or changed to nitric acid by the 
Oswald method. 

253. Relative availability of nitrogen fertilizers.^ — It is 
very difficult to rank nitrogenous fertilizers on the basis of 
their rate of availability, since the conditions within the soil 
so markedly influence the transformations, especially those 
of a biological nature. Dried blood and ammonium sulfate, 
for example, will give almost as quick results in a warm, well 
aerated soil, as far as higher plants are concerned, as sodium 
nitrate. In general, however, the nitrate fertilizers should be 
rated as most readily available, followed in order by ammo- 
nium salts, dried blood, tankage, and similar materials. Such 
substances as wool, hair, and untreated leather waste should 
rank last. 

FERTILIZERS USED FOR THEIR PHOSPHORUS 

Phosphorus is generally present in nature in combination 
with calcium, iron, or aluminum. Some phosphates carry or- 
ganic matter and when thus associated are generally consid- 
ered to decompose more readily when added to the soil. 

254. Bone phosphate (Ca3(P04)2+). — ^Bones were for- 
merly applied to the soil in the raw condition, either ground 
or unground. Most bone as now sold is merely steamed or 
boiled to remove the fat and nitrogenous matter, which is 
used in other ways. Bone-meal comes on the market as a dusty 
powder of characteristic odor. It contains about 27 per cent, 
of phosphoric acid as tricalcium phosphate. Tankage, which 
has already been spoken of as a nitrogenous fertilizer, con- 
tains from 3 to 8 per cent, of phosphoric acid, largely in the 
form of tricalcium phosphate. All bone phosphates are slow- 
acting manures, and should be used in a finely ground form 
and for the permanent benefit of the soil rather than as an 

^ Thome, C. E., Carriers of Nitrogen in Fertilizers; Soil Sci., Vol. 
IX, No. 6, pp. 487-494, 1920. 



COMMERCIAL FERTILIZER MATERIALS 455 

immediate source of phosphorus. In the soil, water charged 
with carbon dioxide sh)wly converts the insoluble tricalcium 
phosphate into the soluble mono-calcium form : 
Ca3(POj2 + 4C0, + 411^0 = CaH,(P0j2 + 2CaH2(C03)2 

255. Rock phosphate^ (Ca3(Po4)a+). — There are many 
natural deposits of mineral phosphates in different parts of 
the world, some of the most important of which are in North 
America. The phosphorus in all of these is in the form of 
tricalcium phosphate, but the materials associated with it 
vary greatly. Rock phosphate may occur in nature as soft 
phosphate, pebble phosphate, boulder phosphate, and hard 
rock phosphate. 

South Carolina phosphate contains from 26 to 28 per cent, 
of phosphoric acid and a very small amount of iron and 
aluminum. As these latter substances interfere with the man- 
ufacture of acid phosphate from rock, their presence is veiy 
undesirable, rock containing more than from 3 to 6 per cent, 
being unsuitable for that purpose. 

Florida phosphates exist in the form of soft phosphate, 
pebble phosphate, and boulder phosphate. Such phosphate 
contains from 18 to 30 per cent, of phosphoric acid, and be- 
cause of its being softer than most of these rocks it is often 
applied to the land without being first converted into a soluble 
form. The other two forms, pebble phosphate and boulder 
phosphate, are highly variable in composition, ranging from 
20 to 40 per cent, in phosphoric acid content. Tennessee 
phosphate, which is now very important, contains from 25 to 
35 per cent, of phosphoric acid. 

Rock phosphate, or floats as it is often called, appears on 

the market as a heavy finely ground powder of light gray 

color. It generally carried about 27 per cent, of phosphoric 

acid as Ca3(,P04)„. A typical analysis is as follows: 

* Waggaman, W. H., and Fry, W. H., Phosphate Bock and Methods 
Proposed for Its Utilisation as a Fertilizer; U. S. Dept. Agr., Bui. 312, 
1915. 



456 NATURE AND PROPERTIES OF SOILS 

Moisture, organic matter, etc 5.06 

Ca3(P0J.. 77.76 

FePO^ and AlPO, 1.50 

CaCOg 4.43 

MgCO. 50 

CaF. 4- CaCl 6.11 

FeS 77 

FcoOg and ALO3 3.87 

Rock phosphate undergoes the same change in the soil as 
bone-meal but generally much more slowly, unless the soil is 
very high in organic matter. Mixing the rock with manure 
seems to hasten its availability to plants. 

256. Acid phosphate ^ (CaH4(P04)o+). — Acid phosphate 
is a dry material of a browning gray color, partially soluble in 
water, and has a characteristic acrid odor. It is intensely 
acid to litmus, as it contains certain acid salts. It carries 
from 14 to 16 per cent, of available P2O5 and small amounts 
of insoluble P2O5. It is made by treating raw rock with sul- 
furic acid under the proper conditions.^ 

CaaCPOJ^ + 2H2SO4 = CaH,(POJo + 2Ca SO4 

(insoluble) (water soluble) 

The acid is never added in amounts capable of quite com- 
pleting this reaction. Some di-calcium phosphate [CagHg 
(FOi)o], spoken of as citrate soluble or reverted phosphoric 
acid, is thus produced. 

CaaiPOJ. + H2SO, = Ca,Ho(POJ. + CaSO^ 
(insoluble) (reverted) 

Acid phosphate consists mostly of gypsum and mono-cal- 
cium phosphate with some di-calcium phosphate and impuri- 

* Chemically, three forms of phosphoric acid are recognized by the 
fertilizer industry: (1) insoluble (Ca.,(PCf4)2), (2) reverted or citrate 
soluble (Ca.H^CPO,),), and (3) water soluble (CaH.CPO,)^. The 
water soluble and citrate soluble phosphates are rated as available to 
plants. The insoluble form is considered as tinavailahle. 

^Waggaman, W. H., The Manufacture of Acid Phosphate; U. S. Dept. 
Agr., Bui. 144, 1914. 



COMMERCIAL FERTILIZER MATERIALS 457 

ties. The water soluble and reverted phosphoric acid are both 
rated as available. 

The phosphates of acid ])hospliate wlicn added to the soil 
quickly revert to an insoluble form : 

CaH,(PO,).> + 2CaH3(C03),=:Ca3(POJ, + 4CO., + 4H,0 
Ca2H3(PO,)", + CaH,(C03),=:Ca3(POj2 + 2C02 + 2H,0 

Plenty of active calcium should be present when acid phos- 
phate is used to insure this reaction instead of the formation 
of the very insoluble ferric phosphate (FeP04) and alumiiium 
phosphate (AIPO4). Acid phosphate does not seem to make 
the soil acid.^ In fact, it is considered by some investigators 
to decrease the acidity by rendering aluminum and iron in- 
soluble. 

257. Basic slag ((CaO)s.Po05.Si02+).— Iron or steel con- 
taining over 2 per cent, of phosphorus is too brittle to be 
useful and, as a consequence, ores of this character were little 
used until methods of removing this phosphoric acid were 
discovered. The use of wood in smelting provided a basic ash, 
thus removing phosphorus from the pig iron. With coal, how- 
ever, the slag is acid and the phosphorus remains with the 
ore. In the open-hearth method of smelting the furnaces are 
lined with a specially prepared dolomitic limestone. Lime is 
later added as the smelting proceeds. The calcium of the 
slag unites with the phosphorus of the iron, thus reducing 
the percentage of that element in the steel. The most prob- 
able formula for the phosphorus compound in basic slag is 
(CaO)5.Po05.Si02. Basic slag contains a large amount of 
iron and calcium hydroxide. Below is a typical analysis : 

CaO 45.0 ALO3 1.7 

MgO 6.2 SiO. 6.9 

FeO -f Fe.O,, 17.6 P,0, 18.1 

MnO 3.5 Other constituents... 1.0 

* Conner, S. D., Acid Soils and the Effect of Acid Phosphate and 
Other Fertilizers Upon Them; Jour. Ind. and Eng. Cliem., Vol. 8, No. 
1, pp. 35-40, 1916. 



458 NATURE AND PROPERTIES OF SOILS 

Basic slag comes on the market as a heavy dark gray pow- 
der, extremely alkaline to litmus, and contains from 14 to 
20 per cent, of P2O5. The phosphorus of basic slag is almost 
all soluble in citric acid and, therefore, is rated as available 
phosphoric acid. It does not revert in the soil as does acid 
phosphate, but is immediately attacked by carbon dioxide and 
rendered rather quickly available. A possible reaction is as 
below : 

(CaO)5.P205-Si02 + 8CO2 + 6H2O = CaH4(POj2 + 
4CaH_.(C03)2 + Si02 

258. Relative availability of phosphate fertilizers. — 

Acid phosphate carries most of its phosphoric acid in a water- 
soluble form and although the phosphates revert to the tri- 
ealcium form immediately when added to the soil, they are 
rather readily available to plants. This is due to the charac- 
ter of the freshly precipitated salt and the surface exposed 
for solution activities. To insure a good distribution in the 
soil of the phosphoric acid and a rapid influence on crops, acid 
phosphate should be well mixed with the soil. 

Basic slag, since its phosphoric acid is largely citrate sol- 
uble, is generally considered as next to acid phosphate in 
availability. Steamed bone-meal usually gives better results 
than raw rock phosphate and rates third, with rock phos- 
phate fourth in availability. The degree of fineness makes a 
great difference in the availability of the less soluble phos- 
phate fertilizers, especially the ground bone and raw rock 
phosphate. The latter material should be ground fine enough 
to pass through a sieve having at least one hundred meshes to 
the inch. 

259. Raw rock phosphate versus acid phosphate. — Con- 
siderable discussion as well as controversy has of late arisen 
regarding the relative merits of acid phosphate and raw rock 
phosphate not only when applied on the basis of equal amounts 
of phosphoric acid but also when compared on the basis of 



COMMERCIAL FERTILIZER MATERIALS 459 

equal money values. If rock phosphate could be made to 
equal or nearly equal the availability of acid phosphate, ob- 
vious advantages would accrue, since raw rock costs much less 
than acid phosphate and carries about twice as much phos- 
phoric acid. 

The availability of the phosphorus of raw rock phosphate 
varies considerably with conditions. At least four major in- 
fluences have been recognized: (1) the character of the crop 
grown, (2) reaction of the soil, (3) the character of accom- 
panying salts, and (4) the decomposition of organic matter. 
It is to be expected that the various kinds of plants should 
not be equally influenced by the phosphorus of tri-calcium 
phosphate. Prianischnikov ^ found that lupines, mustard, 
peas, buckwheat, and vetch responded to fertilization with 
raw rock phosphate in the order named, while the cereals 
did not respond at all. He did not include maize in his ex- 
periments, but that crop is said to respond well to difficultly 
soluble phosphates. It is generally considered that those 
plants which have a long growing season are better able to 
utilize tri-calcium phosphate than are more rapidlj^ growing 
plants. 

A number of investigators have stated, as a result of their 
experimentation, that the availability of raw rock phosphate 
is greater in acid soils than in those strongly basic. If acidity 
of the soil is due to the presence of an actual acid, it is con- 
ceivable that the availability may be due to the solvent action 
of the soil acid on the calcium of the tri-calcium phosphate, 
producing the di-calcium salt which appears to be fairly read- 
ily available to plants. When, however, soil acidity is due 
to a lack of certain active bases, the case is different. Gedroiz ^ 

' Prianischnikov, D., Bericht uber Verschiedene Versuche mit Rohphos- 
phaten unter Reduction ; Moscow, 1910. 

*Gedroiz, K. K., Soils to which Bock Phosphates May Be Applied 
with Advantage; Jour. Exp. Agron. (Russian), Vol. 12, pp. 529-539, 
811-816, 1911. The authors are indebted to Dr. J. Davidson for the 
translation. 



460 NATURE AND PROPERTIES OF SOILS 

explains this on the basis of the absorptive properties of the 
so-called acid soil. He regards rock phosphate, not as a chemi- 
cal compound, but as a solid solution of di-calcium phosphate 
with lime. According to Gedroiz it is this excessive basicity 
of the phosphate which is responsible for its unavailability. 
Absorption of the excess calcium would leave the phosphate 
in a more readily available condition by forming the di- 
calcium salt. 

The presence of certain salts has been found to influence the 
availability of difficultly soluble phosphates. The subject has 
been investigated by a large number of experimenters, and it 
will be possible to summarize their results only in part and 
very briefly. It has been found, for example, that calcium 
carbonate decreases the availability of raw rock phosphate 
and bone-meal. Sodium nitrate reduces the availability of 
the tri-calcium phosphates, while the ammonium salts increase 
their availability. Iron and aluminum salts decrease avail- 
ability. The influence of other salts has not been so well 
worked out. Prianischnikov,^ as the result of his extended 
experiments on the subject, holds that salts from which plants 
absorb acid radicals in larger amounts than they do bases 
decrease availability, or at least do not affect it, while salts 
from which plants absorb the bases in the greater quantity 
have a tendency to render the phosphate more available be- 
cause of the hydrogen ion concentration. 

There has been great differences of opinion among investi- 
gators as to the effect of the decomposition of organic matter 
on the availability of the phosphorus of tri-calcium phosphate. 
The contention that the availability is increased probably 
originated with Stoklasa,^ whose experiments with bone-meal 

^ Prianischnikov, D., fj&er den Einfluss von Kohlensduren Kalk auf die 
WirTcung von VerscJiiedenen Phosphaten; Landw. Vers. Stat., Band 75, 
Seite 357-376, 1911. 

*Stoklasa, J., Duchacek, F., and Pitra, J., uier den Einfinss der Bak- 
terien auf die Knochenzersetsung ; Centrlb. f. Bakt., II, Band 6, Seite 
526-535, 554-558, 1900. 



COMMERCIAL FERTILIZER MATERIALS 461 

indicate that the availability is increased by decay. A large 
number of experiments have been conducted with raw rock 
phosphate composted with stable manure, among which may 
be mentioned those by Hartwell and Pember ^ and also by 
Tottingham and Hoffman,- who, in carefully conducted experi- 
ments, failed to find that the availability of the raw phos- 
phate, as indicated by chemical methods, was increased by 
fermentation with stable manure. Opposing results have also 
been obtained, however, and the evidence is somewhat con- 
flicting. 

With so many factors active in varying the results, espe- 
cially those from raw rock phosphate, it is not surprising that 
satisfactory field data where acid phosphate and raw rock 
are compared are difficult to obtain. Thorne,^ after a critical 
review of the field experiments where acid phosphate and raw 
rock were used, comes to the conclusion that, while raw rock 
phosphate is an excellent fertilizer, acid phosphate is gener- 
ally superior. He finds that, while raw rock may be used 
with profit on land materially deficient in phosphorus, acid 
phosphate has generally proven to be the more effective and 
the more economical carrier of phosphoric acid for crops. 

These conclusions, which are corroborated by other in- 
vestigators,* do not imply that raw rock phosphate is never 
equal or superior to acid phosphate, nor that raw rock does 
not have a place as a fertilizer on the average farm. On a 

* Hartwell, B. L., and Pember, F. R., The Effect of Cow Dung on the 
Availability of Bocic Phosphate; R. I. Agr. Exp. Sta., Bui. 151, 1912. 

' Tottingham, W. E., and Hoffman, C, The Nature of the Changes in 
Solubility and Availability of Phosphorus in Fermenting Mixtures; Wis. 
Agr. Exp. Sta., Res. Bui. '29, 1913. 

'Thome, C. E., Baw Phosphate BocTc as a Fertiliser ; Ohio Agr. Exp. 
Sta., Bui. 305, 1916. 

* Wiancko, A. T., and Conner, S. D., Acid Phosphate versus Baw Bock 
Phospiiate as Fertilizer; Purdue Univ. Agr. Exp. Sta., Bull. 187, 1916. 

Brooks, W. P., Phosphates in Massachusetts Agriculture; Mass. Agr. 
Exp. Sta., Bull. 162, 1915. 

Waggaman, W. H., and Wagner, C. R., Analysis of Experimental 
Work with Ground Baiv Bock Phosphate as a Fertilizer; U. S. Pept. 
Agr., Bui. 699, 1918. 



462 



NATURE AND PROPERTIES OF SOILS 



soil rich in organic matter it may be added to advantage. It 
is especially useful in reinforcing farm manure, seemingly be- 
ing about as effective under such conditions as is acid phos- 
phate. Its higher phosphorus content and lower cost a ton 
gives it an added advantage. The figures from Ohio/ cover- 
ing a period of fourteen years in a rotation of maize, wheat, 
and hay may be taken as evidence regarding these points. 
The manure, reinforced to the ton with 40 pounds of acid 
phosphate and raw rock phosphate, respectively, was applied 
to the corn at the rate of eight tons to the acre. 

Table XCVI 

a comparison of acid phosphate and raw rock in equal 
weights when added to the soil with manure. 



Manxjre 


Average Annual Increase to the 
Acre 




Maize 
14 Crops 


Wheat 
14 Crops 


Hay 
11 Crops 


With raw rock 


25.0 bu. 
30.6 bu. 


12.9 bu. 
15.1 bu. 


1578 lbs. 


With acid phosphate 


1853 lbs. 



FERTILIZERS USED FOR THEIR POTASSIUM 

The production of potassium fertilizers is largely confined 
to Germany, where there are extensive beds varying from 
50 to 150 feet in thickness, lying under an area extending 
from the Harz Mountains to the Elbe River and known as 
the Stassfurt deposits. Large deposits of crude potash salts 
occur in other sections of Germany, and also in France. 
While small deposits occur in other parts of the world the 
French and German mines are at present the only ones of 
any great commercial importance. The World War stimu- 
lated considerable investigation regarding possible sources of 

^Thorne, C. E., et ah, Plans and Summary Tables of the Experiments 
at the Central Farm; Ohio. Agr. Exp. Sta., Circ. 120, p. 112, 1912. 



COMMERCIAL FERTILIZER MATERIALS 463 

potash, especially in the United States. Kelp, saline brines, 
deposits in old lake beds, and flue dust yielded considerable 
potassium. Most of these sources, however, are too expensive 
to compete with European potash in normal times. 

260. Stassfurt salts and their refined equivalents. — The 
Stassfurt salts contain their potassium eitiier as a chloride 
or as a sulfate. The chloride has the advantage of being more 
diffusible in the soil, but in most respects the sulfate is pref- 
erable. Potassium chloride in large applications has an in- 
jurious effect on certain crops, among which are tobacco, 
sugar-beets, and potatoes. On cereals, legumes, and grasses 
the muriate appears to have no injurious effect. 

Kainit is the most common of the crude products of the 
Stassfurt mines and is imported into this country in large 
amounts. It is generally a greyish vari-colored salt, soluble 
in water and alkaline to litmus. It carries from 12 to 14 
per cent, of KoO, largely as potassium sulfate. Its potash 
is immediately available to the crop. Below is a typical 
analysis : 

K2SO4 21.3 NaCl 34.6 

KCl 2.0 CaSO, 1.7 

MgSO^ 14.5 Insolul)le 8 

MgClo 12.4 H2O 12.7 

Silvinit contains its potassium both as a chloride and as a 
sulfate. It also contains sodium and magnesium chlorides. 
Potash constitutes about 16 per cent, of the material. Owing 
to the presence of chlorides, it has the same effect on plants 
as has kainit. There are a number of other Stassfurt salts, 
consisting of mixtures of potassium, sodium, and magnesium 
in the form of chlorides and sulfates. They are not so widely 
used for fertilizers as are those mentioned above. 

A great proportion of the crude salts are refined for ex- 
port purposes, appearing on the market as either the chloride 
or the sulfate. They usually contain from 48 to 50 per cent. 



464 NATURE AND PROPERTIES OF SOILS 

of potash. The chief impurity is common salt. Some of the 
potash salts produced in this country carry boron, which is 
extremely toxic to plants. Such is not generally true of the 
German and French products. 

Potassium chloride and potassium sulfate when added to 
the soil are immediately soluble, being held in the soil solu- 
tion or absorbed either physically or chemically by the col- 
loidal complexes. Due to the selective absorption of the soil 
for the potassium ion and the fact that plants absorb more of 
this ion than of the acid radical, an acid residue tends to re- 
sult from the use of such fertilizers. Some means, such as the 
use of lime, should be employed to counteract this tendency. 

261. Other sources of potash.^ — For some time after the 
use of fertilizers became an important farm practice, wood- 
ashes were the source of most of the potash. They also con- 
tain a considerable quantity of lime and a small amount of 
phosphorus. The product known as unleached wood-ashes 
contains from 5 to 6 per cent, of potash, 2 per cent, of phos- 
phoric acid, and 30 per cent, of calcium oxide. Leached wood- 
ashes contain about 1 per cent, of potash, II/2 per cent, of phos- 
phoric acid, and from 28 to 29 per cent, of lime in the form 
of the hydroxide and carbonate. Unleached ashes carry the 
oxide, hydroxide, and carbonate forms of calcium. Ashes 
contain the potassium in the form of a carbonate, (K2CO3), 
which is alkaline in its reaction and in large amounts may be 
injurious to seeds. Otherwise this form of potash is very de- 
sirable, since no acid residue is left in the soil by its use. 

* Young, G. J., Potash Salts and Other Salines in the Great Basin; 
U. S. Dept. Agr., Bui. 61, 1914. 

Waggaman, W. H., and Cullen, J. A., The Recovery of Potash from 
Alunite; U. S. Dept. Agr., Bui. 415, 1916. 

Hirst, C. T., and Carter, E. G., Some Sources of Potassium; Utah 
Agr. Exp. Sta., Circ. 22, 1916. 

Waggaman, W. H., The Production and Fertiliser Value of Citric- 
Soluble Phosplwric Acid and Potash; U. S. Dept. Agr., Bui. 143, 
1914, 

Ross, W. H., et al., The Recovery of Potash as a By-Product in the 
Cement Industry; U. S. Dept. Agr., Bui. 572, 1917. 



COMMERCIAL FERTILIZER MATERIALS 465 

Ashes are beneficial to acid soils through the action of both 
the potassium and calcium salts. 

Insoluble forms of potassium, existing in many rocks 
usually in the form of a silicate, are not regarded as having 
any manurial value. Experiments with finely ground feld- 
spar have been conducted by a number of investigators, but 
have, iji the main, offered little encouragement for the suc- 
cessful use of this material. Leucite and alunite have given 
but little better results. An insoluble form of potassium is 
not recognized as of value when a fertilizer is rated on the 
basis of chemical analysis. 

During the World War, since the German importation of 
potash salts ceased, potassium was sought commercially from 
a number of sources in this country. Alunite, a hydrous sul- 
fate of aluminum and potassium, has been experimented with 
to some extent as have also the green-sand marls which carry 
glauconite. In a number of cases the recovery of potash 
from flue dust has proven commercially profitable. It is esti- 
mated that 87,000 tons of potash are lost yearly from cement 
kilns alone in the United States and Canada. During the war 
considerable progress was made in harvesting and drying the 
kelp which grows off the coast of southern California. The 
kelp was later extracted for its potash. This source of potas- 
sium is rather expensive, however, when brought into com- 
petition with European products. 

Perhaps the most reliable sources of domestic potash are 
the brines of certain alkali lakes of western United States and 
from the deposits in old lake beds in the same region.^ The 
exploitation of such sources will, of course, depend upon the 
price at which German potash can be laid down in this 
country. 

^ Such salts unless properly prepared are likely to contain borax 
which is usually toxic when applied at a greater rate than five pounds 
to the acre, the influence being more intense at low soil moisture. 

Neller, J. E., and Morse, W. J., Effects upon the Growth of Potatoes, 
Corn and Beans, Eesultinq from the Addition of Borax to the Fertilizer 
used; Soil Sci., Vol. XII, 'No. 2, pp. 79-105, 1921. 



466 NATURE AND PROPERTIES OF SOILS 

SULFUR AND SULFATES AS FERTILIZERS ^ 

The use of these substances as a means of increasing plant 
growth when applied to soils has recently received much at- 
tention. While sulfates have been used for centuries as a 
soil amendment, it is only within the last f cav years that sulfur 
itself has been applied to soil. The question of the effect of 
the latter has received considerable study, not only in France 
and Germany but in this country as well. The influence of 
both sulfur and sulfates may be a direct nutrient relationship 
or the action may be that of a soil amendment. Only in case 
the former influence occurs could these materials be rated as 
fertilizers. 

262. The use of free sulfur. — Boullanger ^ in 1912 added 

* Another group of fertilizers may be mentioned — the so-called catalytic 
fertilisers. Such materials are supposed to aid plant growth by accelerat- 
ing natural soil processes. The catalytic action of any material is very 
difficult to establish when it is added to the soil, since the soil itself 
carries many substances of a catalytic nature. Manganese has been most 
seriously considered as a catalytic fertilizer. 

Konig, J., Hasenbaumer, J., and Coppenrath, E., Einige Neue Eigen- 
schaften des Ackerbodens ; Landw. Vers. Stat., Band 63, Seite 471-478, 
1905-1906. 

May, D. W., and Gile, P. L., The Catalase of Soils; Porto Eico Agr. 
Exp. Sta., Circ. 9, 1909. 

Sullivan, M. X., and Eeid, F. E., Studies in Soil Catalysis; U. S. 
Dept. Agr., Bur. Soils, Bui. 86, 1912. 

Konig, J., Hasenbaumer, J., and Coppenrath, E., Beziehungen zwischen 
den Eigenschaften des Bodens und der Nahrstoff'aufnahme durch die 
pflanzen; Landw. Vers. Stat, Band 66, Seite 401-461, 1907. 

Kelly, M, P., The Influence of Manganese on tJie Growth of Pine- 
apples'; Jour. Ind. and Eng. Chem., Vol. I, p. 5.3.3, 1909. 

Sullivan, M. X.^ and Eobinson, W. O., Manganese as a Fertilizer; 
U. S. Dept. Agr., Bur. Soils, Circ. 75, 1912. 

Skinner, J. J., and Sullivan, M. X., The Action of Manganese in Soils; 
U. S. Dept. Agr., Bui. 42, 1914. 

Skinner, J. J., and Eeid, F. E., The Action of Manganese Under Acid 
and Neutral Soil Conditions ; U. S. Dept. Agr., Bui. 441, 1916. 

Bertrand, G., The Action of Chemical Infinitesimals in Agriculture ; 
Address before 8th Inter. Cong. App. Chem., New York, 1912. 

Eoss, W. H., The Use of Radioactive Substances as Fertilizers; U. S. 
Dept. Agr., Bui. 149, 1914. 

Hopkins, C. G., and Sachs, W. H., Radium as a Fertilizer; 111. Agr. 
Exp. Sta., Bui. 177, 1915. 

^Boullanger, E., Action du soufre en fleur sur la vegetation; Compt. 
Rend. Acad. Sci. Paris, T. 154, pp. 369-370, 1912. 



COMMERCIAL FERTILIZER MATERIALS 467 

flowers of sulfur to a soil at the rate of 23 parts per million 
of soil. He obtained increased growth in all treated soils on 
which carrots, beans, celery, lettuce, sorrel, chicory, potatoes, 
onions, and spinach were grown, the weights of the crops on 
the treated soil being from 10 to 40 per cent, greater tlian those 
on the untreated soil. On soils that had been sterilized before 
applying sulfur, the effect was less marked, from which he 
concludes that the beneficial effects were due to the influence 
of the sulfur on the micro-organisms of the soil. There may 
be some question, however, whether this conclusion is justi- 
fiable. Sulfur was found by Boullanger and Dugardin ^ to 
favor ammonification in soils. Beneficial effects from the use 
of free sulfur have also been obtained by Demelon,- and by 
Bernhard,^ while von Feilitzen ^ found it to be ineffective as 
a fertilizer. 

In this country, Shedd ^ of Kentucky obtained increases in 
tobacco yield with sulfur. Perhaps the most marked results 
with sulfur are reported by Reimer and Tartar ® from Oregon. 
Alfalfa and clover yields were increased from 50 to 100 per 
cent. 

That free sulfur may, under certain conditions, exert a ben- 
eficial influence on plant growth must be conceded, but that 
the action is a direct nutritive one remains to be proven. 
Free sulfur is insoluble and cannot be absorbed as such by 
plants. It readily undergoes oxidation, however, producing 
the sulfate, as already explained under sulfofication. As such 

^Boullanger, E., and Dugardin, M., Mecanisme de V action fertilisante 
du soufre; Compt. Eend. Acad. Sei. Paris, T. 155, pp. 327-329, 1912. 

^Demelon, A., Sur I'action fertilisante du soufre; Compt. Rend. Acad. 
Sci. Paris, T. 154, pp. 524-526, 1912. 

' Bernhard, A., Versuche iiher dis Wirlcung des Schivefels als Bung im 
Jahre 1911; Deutsche Landw. Presse., Band 39, S. 275, 1912. 

*von Feilitzen, H., ijier die Verwendung der Schivefelblute sur Be- 
kampfung des Eartoffelschorfes und als indirlctes Dungemittel ; Puhling's 
Landw. Zeit., Band 62, Seite 7, 1913. 

° Shedd, O. M., The Relation of Sulfur to Soil Fertility: Kv. Agr. Exp. 
Sta., Bui. 188, 1914. 

'Reimer, F. C, and Tartar, H. V., Sulfur as a Fertilizer for Alfalfa 
in Southern Oregon; Ore. Agr, Exp. Sta.. BuL 163, 1919. 



468 



NATURE AND PROPERTIES OF SOILS 



a reaction tends to encourage soil acidity, injurious influ- 
ences may easily occur on soils already acid or possessing only 
small quantities of active calcium and magnesium. If sulfur 
functions as a fertilizer, it is by a change to the sulfate, in 
which form it is absorbed by plants. 

263. The use of sulfate sulfur. — The experimental evi- 
dence regarding the direct fertilizer influence of sulfate sulfur 
is much more difficult to interpret than that regarding flowers 
of sulfur. Gypsum has been applied to soils for centuries 
and marked influences on crop growth are of common observa- 
tion. Whether this stimulation is due to the sulfate or to the 
base which accompanies it cannot be determined. Even if the 
sulfate influence could definitely be proved, there would still 
remain the question as to whether the action was direct or 
indirect. 

264. Relation of sulfur to soil fertility. — The possible 
deficiency of sulfur in arable soils was first established by 
Hart and Peterson.^ They point out that crops remove more 

Table XCVII 

pounds sulfur trioxide and phosphorus pentoxide 

removed to the acre by average crops. 



Crop and Yield to the Acre 



Pounds to the Acre 



S03 


P20„ 


15.7 


21.1 


14.3 


20.7 


19.7 


19.7 


12.0 


18.0 


64.8 


39.9 


92.2 


33.1 


98.0 


61.0 


11.5 


21.5 


11.3 


12.3 



Wheat (30 bu.) 

Barley (40 bu.) 

Oats (45 bu.) 

Corn (30 bu.) 

Alfalfa (9000 lbs. air dry) 

Turnips (4657 lbs. air dry) . . . . 

Cabbage (4800 lbs. air dry) 

Potatoes (3360 lbs. air dry) 

Meadow hay (2822 lbs. air dry) 



* Hart, E. B., and Peterson, W. H., Sulfur Requirements of Farm Crops 
in Relation to the Soil and Air Supply; Wis. Agr. Exp. Sta., Ees. Bui. 
14, 1911. 



COMMERCIAL FERTILIZER MATERIALS 469 

sulfur from the soil than is indicated by the earlier analyses 
of plant ash, since considerable sulfur was lost by volatization 
in the former determination. On the basis of their own 
methods, they present the data given as to the removal of 
sulfur trioxide and phosphoric acid from the soil by average 
crops. (See Table XCVII, page 468.) 

It is to be noted that the amount of sulfur removed by crops 
is generally about equal to and in some cases much in excess 
of the phosphoric acid taken from the soil. The fact that 
soils are generally as low in sulfur as in phosphoric acid lends 
weight to the argument, that if the latter is a limiting factor 
in productivity the former should be also. 

To ascertain whether the supply of sulfur in the soil is 
really depleted by cropping, Hart and Peterson made parallel 
determinations of sulfur in five virgin soils and in five soils of 
the same respective types that had been cropped for sixty 
years. In each type the cropped soil contained less sulfur 
than the virgin soil, the average for the former being .053 
per cent. SO3 and for the latter .085 per cent. SO3. 

Considerable sulfur is added to the soil every year in the 

rain-water, largely in the sulfate form, although near cities 

appreciable amounts of hydrogen sulfide and sulfur di-oxide 

are formed. The amount of such sulfur is variable. Miller,^ 

at the Rothamsted Experiment Station, reports 17.4 pounds 

of SO3 to the acre, while Crowther and Ruston ^ near Leeds, 

England, found 161 pounds of SO3 to the acre. Peck ^ found 

the addition of SO3 to be at the rate of 1 pound to the acre a 

month at Mt. Vernon, Iowa, while Trieschmann,* over a 

^ Miller, N. H. J., TJie Amount of Nitrogen, as Ammonia and as 
Nitric Acid, and of Chlorine in the Rain-Water Collected at Rotham- 
sted; Jour. Agr. Sci., Vol. I, pp. 280-303, 1905. 

* Crowther, C, and Ruston, A. C, The Nature, Distribution and 
[Effect Upon Vegetation of Atmospheric Impurities In and Near an 
Industrial Town; Jour. Agr. Sci., Vol. 4, pp. 25-55, 1911. 

^Peck, E. L., Nitrogen, Chlorine and Sulfates in Bain and Snoiv; 
Chem. News., Vol. 116, p. 283, 1917. 

* Trieschmann, J. E., Nitrogen and other Compounds in Bain and 
Snow; Chem. News, Vol. 119, p. 49, 1919. 



470 NATURE AND PROPERTIES OF SOILS 

different period at the same place, determined the addition to 
be less than .2 pound a month. Stewart,^ at the University 
of Illinois, reports the addition of sulfur as SO3 over a period 
of seven years as amounting to 9.4 pounds of SO3 monthly to 
the acre or 113 pounds yearly. 

The loss of sulfur expressed as SO3 from the Cornell lysi- 
meters,- due to cropping and drainage combined, amounted, 
over a period of ten years, to 149.5 pounds from an acre 
yearly from the rotation tanks. The addition of sulfur in the 
rain-water at Ithaca amounts to about 65.4 pounds of SO3 
each year. It is, therefore, safe to assume that rain-water will 
not replace the sulfur removed by normal cropping and 
leaching. It must be remembered, however, that in rational 
soil management, sulfur is returned to the soil in green- 
manures, crop residues and farm manures. Commercial fer- 
tilizers are now very commonly used, especially acid phos- 
phate, which is about one-half gypsum. At the Ohio Experi- 
ment Station,^ plats treated with sulfate bearing fertilizers 
were found over a period of years to contain considerably 
more sulfur than soils not so fertilized but cropped in a 
similar manner. 

In the light of such data it seems that the sulfur problem 
is not comparable with or as serious as the phosphorus prob- 
lem of soil fertility. By the careful utilization of the normal 
residues produced on the farm there seems little reason for 
sulfur being a limiting factor in soil productivity, especially 
if fertilizers carrying sulfur are used in connection with a 
rational system of soil management. 

^Stewart, E., Sulfur in Belation to Soil Fertility; 111. Agr. Exp. Sta., 
Bui. 227, 1920. 

* Complete data on these lysimeters will be found in par. 163 of this 
text. 

^ Ames, J. W., and Boltz, G. E., Sulfur in delation to Soils and Crops; 
Ohio Agr. Exp. Sta., Bui. 292, 1916. 



CHAPTER XXIII 
THE PRINCIPLES OF FERTILIZER PRACTICE ^ 

The use of commercial fertilizers has increased so rapidly 
within the last decade that specific knowledge is needed re- 
garding the various materials offered for sale in order that 
the most economical results may be attained. The greater 
the general knowledge, both practical and theoretical, that a 
person possesses as to the effects of the different nutrient con- 
stituents on plant growth, the more rational will be the fer- 
tilizer use. Fertilizer inspection and control, principles of 
buying and home-mixing, methods of applicatiop, mixtures for 
special crops, are a few of the many phases of economical 
fertilizer practice. The final and vital consideration is re- 
garding the financial return from fertilizer application. A 
fertilizer should always pay. 

As all fertilizers exert, either directly or indirectly, a resid- 
ual effect, the problem necessarily broadens into a study of 
the systems of applying them to a series of crops or to a rota- 
tion, rather than a study of the effects of one particular fer- 
tilizer application on one particular crop. 

265. Influence of nitrogen on plant growth.^ — Of the 
three elements carried in an ordinary complete fertilizer, 

*Hall, A. D., Fertilizers and Manures; New York, 1921. 
Halligan, J. E., Soil Fertility and Fertilizers ; Easton, Pa., 1912. 
Van Slyke, L. L., Fertilizers and Crops; New York, 1912. 
Fraps, G. S., Principles of Agricultural Chemistry; Easton, Pa., 1913. 
* Discussions of the effects of the various elements on plants may be 
found as follows: Eussell, E. J., Soil Conditions and Plant Growth, 
Chapter II, pp. 19-50; London, 1912. Also, Hall, A. D., Fertilizers and 
Manures, Chapters III, IV and VI; New York, 1921. 

471 



472 NATURE AND PROPERTIES OF SOILS 

nitrogen ^ seems to have the quickest and most pronounced 
effect, not only when present in excess of other constituents, 
but also when moderately used. It tends primarily to encour- 
age above ground vegetative growth and to impart to the 
leaves a deep green color, a lack of which is usually due to 
insufficient nitrogen. It tends in cereals to increase the 
plumpness of the grain, and with all plants it is a regulator 
in that it governs to a certain extent the utilization of potash 
and phosphoric acid. Its application tends to produce succu- 
lence, a quality particularly desirable in certain crops. In its 
general effects it is very similar to moisture, especially when 
supplied in excessive quantities. 

The peculiarity of nitrogen lies not only in its absolute ne- 
cessity for plant growth, its stimulation of the vegetative 
parts, and its close relationship to the general tone and vigor 
of the crop, but also in the fact that it was not one of the 
original elements of the earth's crust. During the formation 
of the soil it slowly and gradually became present, brought 
down by rains and fixed naturally in the soil through the 
agency of bacterial action. Now it exists in complex nitrog- 
enous compounds of the more or less decayed organic matter, 
and becomes available to plants largely through bacterial 
activity. 

It may be stated with certainty that one of the possible 
limiting factors to crop growth is a lack of water-soluble nitro- 
gen at critical periods in amounts necessary for normal devel- 
opment. Since soluble nitrogen may be very readily lost 
from the soil by leaching, the problem of proper plant nutri- 
tion becomes a serious one. Not only must the farmer be able 
so to regulate the addition of nitrogen in fertilizers as to obtain 
the highest efficiency, but he must understand the control and 

* For a discussion of nitrogen in relation to crop yield, see Hunt, T. F., 
■ The Importance of Nitrogen in the Growth of Plants; Cornell Agr. 
Exp. Sta., Bui. 247, 1907. 



THE PRINCIPLES OF FERTILIZER PRACTICE 473 

encouragement of the natural fixation as well. Due to the 
practical possibility of keeping up the nitrogen supply of the 
soil by the proper use of farm manure, crop residues, green- 
manures, and the utilization of legumes in the rotation, the 
quantity of nitrogen purchased in commercial fertilizers 
should be as small as possible if its use is to be profitable. 
When so purchased it should function more or less as a crop 
starter rather than as a source of any large amount of the 
plants' supply of nutrient. The emphasis i)laced on all phases 
of the nitrogen problem serves to reveal its great importance 
in fertility practices. 

Because of the immediately visible effect from the applica- 
tion of soluble nitrogen, the average farmer is prone to ascribe 
too much importance to its influence in proper crop develop- 
ment. This attitude is unfortunate, since nitrogen is the 
highest priced constituent of ordinary fertilizers and should 
usually be purchased to a less extent than potash and espe- 
cially than phosphoric acid. Moreover, of the three common 
fertilizer elements, it is the only one which, added in excess, 
will result in harmful after-effects on the crop. These pos- 
sible and important detrimental effects of nitrogen may be 
listed as follows : 

1. 7^ may delay maturity by encouraging vegetative 
growth. This oftentimes endangers the crop to frost, or may 
cause trees to winter badly, 

2. It may weaken the straw and cause lodging in grain. 
This is due to an extreme lengthening of the internodes, and 
as the head fills the stem is no longer able to support the in- 
creased weight, 

3. It may lower quality. This is especially noticeable in 
certain grains and fruits, as barley and peaches. The ship- 
ping qualities of fruits and vegetables are also impaired. 

4. It may decrease resistance to disease. This is probably 
due to a change in the physiological resistance within the 



474 NATURE AND PROPERTIES OF SOILS 

plant, and also to a thinning of the cell-wall, allowing a more 
ready infection from without. 

While certain plants, as the grasses, lettuce, radishes, and 
the like, depend for their usefulness on plenty of nitrogen, it 
is generally better to limit the amount of nitrogen for the 
average crop so that growth may be normal. This results in 
a better utilization of the nitrogen and in a marked reduction 
of the fertilizer cost for a unit of crop growth. This is a 
vital factor in all fertilizer practice, and shows immediately 
whether nitrogen fertilization is or is not an economic success. 

266. Influence of phosphorus on plant growth. — It is 
difficult to determine exactly the functions of phosphoric acid 
in the economy of even the simplest plants. Neither cell divi- 
sion nor the formation of fat and albumen go on to a suffi- 
cient extent without it. Starch may be produced when it is 
lacking, but will not change to sugar. As grain does not form 
without its presence, it very probably is concerned in the pro- 
duction of nucleoproteid materials. Its close relationship to 
cell division may account for its presence in seeds in compara- 
tively large amounts. 

Phosphoric acid hastens the maturity of the crop by its 
ripening influences. This effect is especially valuable in wet 
years and in cold climates where the season is short. The use 
of acid phosphate is being advocated in the Middle West, espe- 
cially for maize, as an insurance against frost-injury and a 
means of avoiding soft corn. Phosphoric acid also encourages 
root development, especially of lateral and fibrous rootlets. 
This renders it valuable in such soils as do not encourage root 
extension and to such crops as naturally have a restricted root 
development. Phosphoric acid is especially valuable for fall- 
sown crops, such as wheat. A sturdy root growth is developed 
which tends to prevent winter injury and prepares the plant 
for a rapid spring development. 

Phosphoric acid decreases the ratio of straw to grain in 
cereals. It also strengthens the straw, thus decreasing the 



THE PRINCIPLES OF FERTILIZER PRACTICE 475 

tendency to lodge, which is likely to occur especially with 
oats if too much available nitrogen is present. In certain 
cases, phosphoric acid decidedly improves the quality of the 
crop. This has been recognized in the handling of pastures 
in England and France. The effect on vegetables is also 
marked. Phosphorus is also known to increase the resistance 
of some plants to disease, due possibly to a more normal cell 
development. In this respect phosphoric acid counteracts the 
influence of a heavy nitrogen ration. 

Excessive quantities of phosphoric acid ordinarily have no 
bad effect, as phosphorus does not stimulate any part unduly, 
nor does it lead to a development which is detrimental. The 
lack of phosphoric acid is not apparent in the color of the 
plants as in the case of nitrogen, and as a consequence phos- 
phoric acid starvation may occur without any suspicion there- 
of being entertained by the farmer. 

One of the most important phases to be noted from this 
comparison of the effects of nitrogen and phosphorus is the 
balancing powers of the latter on the unfavorable influences 
generated by the presence of an undue quantity of the former. 
The possible detrimental effects of too much nitrogen have 
already been noted. This relationship between the phosphorus 
and nitrogen in plant nutrition is very important in fertilizer 
practice, since normal fertilizer stimulation generally results 
in the most economical gains. 

267. Effects of pota-ssium on plant growth. — The pres- 
ence of plenty of available potash in the soil has much to do 
with the general tone and vigor of the plant. By increasing 
resistance to certain diseases it tends to counteract the ill 
effects of too much nitrogen, while in delaying maturity it 
works against the ripening influences of phosphoric acid. In 
a general way, it exerts a balancing effect on both nitrogen 
and phosphate fertilizer materials, and consequently is espe- 
cially important in a mixed fertilizer, if the potash of the 
soil is lacking or unavailable. 



476 NATURE AND PROPERTIES OF SOILS 

Potash is essential to starch formation, either in photo- 
synthesis or in translocation, and is necessary in the develop- 
ment of chlorophyll. It is important to cereals in grain for- 
mation, giving plump heavy kernels. As with phosphorus, it 
may be present in large quantities in the soil and yet exert 
no harmful effect on the crop. While potassium and sodium 
are similar in a chemical way, sodium cannot take the place 
of potash in plant nutrition. Where there is an insufficiency 
of potash, however, sodium seems in some way, either directly 
or indirectly, to be useful.^ 

268. The element in the "minimum." — In connection 
with the obvious importance of utilizing, for any particular 
soil and crop, a fertilizer well balanced as to the three primary 
elements, two queries naturally arise. These are: (1) What 
are the proper proportions of nitrogen, phosphoric acid, and 
potash to apply under given conditions? (2) What would 
be the effect if any one of these should not be present in suffi- 
cient quantity as to make it equal in function to the others ? 

The first query cannot be disposed of until the question of 
fertilizer mixtures has been considered. The second, how- 
ever, is not affected by so many factors, and is more clearly 
a question of the function of the elements concerned and is 
logically discussed at this point. 

Any element that exists in relatively small amounts as com- 
pared with the other important nutrient constituents natur- 
ally becomes the controlling factor in plant development. 
Any reduction or increase in this element will cause a corre- 
sponding reduction or increase in the crop yield. This ele- 
ment, then, is said to be "in the minimum." In fertilizer 
practice, ideal conditions would exist if no constituent func- 
tioned as a decided minimum and the entire influence of each 
single element was fully utilized. In other words, the fertil- 
izer would be balanced as to its relationship to normal plant 

^Hartwell, B. L., and Damon, S. C, The Value of Sodium when 
Potassium is Insufficient ; E. I. Agr. Exp. Sta., Bui. 177, 1919. 



THE PRINCIPLES OF FERTILIZER PRACTICE 477 

growth. That such a condition is more or less ideal and is 
seldom realized is obvious, from the fact that the various fer- 
tilizer carriers undergo more or less radical changes after 
being applied to the soil. The composition of the soil itself 
is also a disturbing factor. Nevertheless, the nearer an ap- 
proach can be made to such conditions, the greater will be the 
economy in fertilizer practice. 

Numerous persons have investigated the question as to what 
effect an increase of an element in the minimum may have on 
crop yield, and various ideas have been advanced to explain 
the effect. The idea of a definite law governing the increase 
of plant growth according as the element in the minimum is 
increased, was first suggested by Liebig. Wagner ^ later 
stated definitely that up to a certain point the increase yield 
was proportional to the increase in the application. This, 
however, evidently cannot apply except over a very limited 
field, since it is a matter of common observation that increased 
crop yield becomes lower as the lacking element is continu- 
ously supplied. 

Mitscherlich ^ has formulated a law which is a logarithmic, 
rather than a direct, function of the increase in the element 
occupying the position of the minimum. Mitscherlich 's law 
may be stated concisely as follows : the increased growth pro- 
duced by a unit increase of the element in the minimum is 
proportional to the decrement from the maximum. In other 
words, the increase is proportional to the difference between 
the actual yield and the possible yield at which the element 
ceases to be a limiting factor. 

Mitscherlich has proposed a definite formula for such a 

* Wagner, H., Beitrdge zur DungerleJire ; Landw. Jahr., Band 12, 
Seite 691 ff., 1883. 

^ Mitscherlich, E. A., Bas Gesetz des Minimums und das Gesetz des 
Abnehmen den Bodenertrages ; Landw. Jahr., Band 38, Seite 537-552, 
1909. 

Also, Ein Beitrage zur Erforschung der Ausnutzung des im Minimum 
Vorliandenen Ndhrstoffes durch die Pflanze; Landw. Jahr., Band 39, 
Seite 133-156, 1910. 



478 NATURE AND PROPERTIES OF SOILS 

growth curve.^ This formula has been questioned by several 
investigators,^ who have shown that a number of conditions, 
such as light, heat, and moisture, tend to disturb the applica- 
tion of such a law. The fact that crop yield is the summation 
of so many varying factors seems to argue in favor of no hard 
and fast rule regarding the increased growth due to the added 
increments of an element in the minimum. It is enough, in 
the practical utilization of fertilizers, to remember that in 
order to obtain the best results from fertilizers a mixture 
should be used that is approximately balanced so far as the 
effects of the nutrients are concerned, the crop as well as the 
chemical constitution of the soil being considered. 

269. Fertilizer brands. — In an attempt to meet the de- 
mands for well-balanced fertilizers suited to various crops and 
soils, manufacturers have placed on the market a large num- 
ber of brands of materials containing usually at least two of 
the important nutrient elements, and nearly always the three ; 
the former being designated as incomplete fertilizers, while 
the latter are spoken of as complete. These various brands 
usually have a significant name,^ which frequently implies the 
usefulness of the material for some special crop growing on a 
particular soil. Oftener, however, the brand name bears no 
relation either to crop or soil. The name should always be 
ignored in fertilizer purchase, the availability and composi- 
tion being the important considerations. 

— — =(a — y)k. Integrating, log (a — y) = c — kx. 

QX 

y=r total yield from any number of increments. 

X z= amount of any particular fertilizer constituent utilized. 

a = maximum yield and is a constant. 

k = a constant depending on y and x, variables. 

='Pfeiffer, Th., Blanck, E., and Flugel, M., Wasser und Licht als Veffe- 
tationsfaMoren und ihre Besiehungen sum Gesetze vom Minimum; 
Landw. Ver. Stat., Band 76. Seite 211-223, 1912. 

Also, Maze, P., Eecherches sue les Eelations de la Plante avec les 
Elem-ents Nutritifs der Sol; Compt. Eend., Tome 154, pp. 1711-1714, 
1912. 

'Potato and Corn Fertilizer, Golden Harvest, Ureka Corn Special, 
Blood and Bone, Harvest King, Soil Builder and the like. 



THE PRINCIPLES OF FERTILIZER PRACTICE 479 

A brand of fertilizer is usually made up of a number of 
materials containing the important nutrient ingredients. 
These materials, already described, are called carriers. The 
making-up of a commercial fertilizer consists in mixing the 
various carriers together so that the required percentages of 
ammonia, potash, and phosphoric acid are obtained, care being 
taken that no detrimental reaction shall occur and that a 
physical condition consistent with easy distribution shall be 
maintained. Brands of fertilizer put out by reputable com- 
panies carry a large proportion of their nutrients in a readily 
available form. A fertilizer made up principally of dried 
blood, tankage, acid phosphate, and kainit or muriate of pot- 
ash is a good example of the ordinary composition of ready 
mixed goods. 

The various brands on the market, besides being complete 
or incomplete, may be designated as high-grade or low-grade 
as to availability, or high-grade or low-grade as to amount of 
plant nutrients carried. In the fertilizer trade the terms 
generally refer to the latter condition. A low-grade fertilizer 
in the latter sense is always encumbered with a large amount 
of inert material, called filler, which adds to the cost of mix- 
ing, transportation and handling. A low-grade fertilizer is 
generally more expensive a unit of nutrient obtained than 
are higher grade goods, and consequently should be avoided. 

Fertilizer concerns have always found it more profitable to 
sell ready mixed fertilizers than to deal in the separate car- 
riers, such as dried blood, muriate of potash, and the like. Of 
late years, however, it has been possible to buy the separate 
materials. The conditions during the World War greatly 
encouraged the application directly to the soil of separate 
carriers, especially acid phosphate, since potash was almost 
unobtainable and nitrogen fertilizers were very high in price. 
The use of phosphoric acid alone is often much more eco- 
nomical and rational than the use of a complete mixture, since 
the nitrogen removed from the soil by normal cropping and 



480 NATURE AND PROPERTIES OF SOILS 

drainage may be replaced in other and more practical ways. 
By maintaining the soil organic matter the natural supply of 
potash may in a loamy or clayey soil often be so influenced 
as to render a potash fertilizer unnecessary. At least there 
may be enough soil potash available so that the use of a com- 
mercial form will not be profitable. 

270. Fertilizer inspection and control. — From the fact 
that so many opportunities are open for fraud either as to 
availability or as to the actual quantities of ingredients pres- 
ent, laws have been necessary for controlling the sale of fer- 
tilizers. These laws apply not only to the ready mixed goods 
but to the separate carriers as well. Most states have such 
laws, the western laws generally being superior to those in 
force in eastern states, where the fertilizer sale is heavier. 
This is because the western regulations are more recent and 
the legislators have had the advantage of the experience gained 
where fertilizers have long been used. Such laws are a pro- 
tection not only to the public but to the honest fertilizer com- 
pany as well, since spurious goods are kept off the market. 

Certain provisions are more or less common to most fer- 
tilizer laws. In general, all fertilizers selling for a certain 
price or over must pay a state license fee or a tonnage tax and 
print the following data on the bag or on an authorized tag : 

1. Number of net pounds of fertilizer to a package. 

2. Name, brand, or trade-mark. 

3. Name and address of manufacturer. 

4. Chemical composition or guarantee. 

For the enforcement of such laws the states usually pro- 
vide adequate machinery. The inspection and analyses may 
be in the hands of the state department of agriculture, of the 
director of the state agricultural experiment station, of a 
state chemist, or under the control of any two of these. In 
any case, a corps of inspectors is provided, the members of 
which take samples of the fertilizers on the market throughout 
the state. These samples are analyzed in laboratories provided 



THE PRINCIPLES OF FERTILIZER PRACTICE 481 

for the purpose, in order to ascertain whether the mixture is 
up to guarantee. The expense of the inspection and control of 
fertilizers is usually defrayed by the license fee or the ton- 
nage tax. 

If the fertilizer falls below the guarantee, — allowing, of 
course, for the variation permitted by law, — the manufacturer 
is subject to prosecution in the state courts. A more effective 
check on fraudulent guarantees, however, is found in pub- 
licity. The state law usually provides for the publication 
each year of the guaranteed and found analyses of all brands 
inspected. Not only has this proved effective in preventing 
fraud, but it is really a great advantage to the honest manu- 
facturer, as his guarantees receive an official sanction. The 
found analysis of most fertilizers is generally above the 
guarantee. 

271. The fertilizer guarantee. — Every fertilizing mate- 
rial, whether it is a single carrier or a complete ready -to-apply 
mixture, must carry a guarantee. The exact form is gener- 
ally determined by the state in which the fertilizer is offered 
for sale. The content of nitrogen is almost invariably ex- 
pressed in terms of ammonia (NH3), although the amount of 
total nitrogen is sometimes required in addition. The phos- 
phorus is quoted in terms of phosphoric acid (P2O5). In 
some cases, a bone-phosphate of lime (B. P. L. or Ca3(P04)2) 
equivalent is included. The guarantee of a simple fertilizer 
material is easy to interpret, since the name of the material is 
printed on the bag or tag. When the amount of the nutrient 
element carried is noted, the availability and general value 
of the goods is immediately known. If the material is sodium 
nitrate at 18 per cent, ammonia, it is apparent that the fer- 
tilizer is high-grade and should give immediate and definite 
results when properly applied to a growing crop. 

The interpretation of a complete fertilizer analysis is not 
as easy, however, since the names of the carriers are seldom 
included in the guarantees. The simplest form of guarantee 



482 NATURE AND PROPERTIES OF SOILS 

is a mere statement of the percentages of NH3, P2O5 and KgO, 
as, for example, a 2 — 8 — 2} This, however, is too brief for a 
guaranteed analysis on goods exposed for sale, as it gives no 
idea whatsoever regarding the solubility of the materials. As 
might be expected, there is a wide range in the character of 
the guarantees required by the various states. For example, 
some states insist on the statement of the percentage of both 
nitrogen and ammonia, while others insist only on the percent- 
age of nitrogen. Some require the soluble, the reverted, and 
the total phosphoric acid, while others require only the soluble 
and the reverted. As to potash, in some cases the soluble 
must be stated, while in other cases the total must be given.- 
In general, a guarantee should show not only the amount 
of the various constituents but also their form or availability. 
The following outline analysis is excellent in this respect : 

Percentage of NH3 as nitrate. Percentage of P2O5 soluble 
Percentage of NHg as ammonia. in water. 
Percentage of NH3 total. Percentage of P2O5 reverted. 

Percentage of K^O water soluble. Percentage of P2O5 as 
Percentage of K^O as chloride. insoluble. 

272. The buying of mixed goods. — The successful buying 
of mixed fertilizers on the retail market depends on two 
things: (1) the selection of a composition suitable to soil and 
crop with carriers of known value; and (2) the purchase of 
high-grade goods. The farmer who observes these points will 
at least have purchased successfully. Whether he obtains a 

' In the South, the order is different. An 8-3-2 means 8 per cent, of 
PA, 3 per cent, of NH, and 2 per cent, of K^O. 

' Below is the guarantee of a complete fertilizer : 

Nitrogen 4.2% 

Equal to ammonia 5.0 

Soluble PA 4.0 

Keverted P2O5 2.0 

Available PsO^ 6.0 

Insoluble P2O5 1.0 

Total PA 7.0 

Water soluble K,0 3.0 



THE PRINCIPLES OF FERTILIZER PRACTICE 483 

profit from the use of the fertilizer depends on the interrela- 
tion of a number of factors more or less variable from season 
to season. 

The selection of a suitable fertilizer, as to carriers and com- 
position, entails, after the need of the crop and soil are de- 
cided, a careful study of the guarantee. Should the guarantee 
be such as that just cited, a large amount of information is 
at hand concerning the forms of the carriers and the availa- 
bility of the important constituents. This knowledge, prop- 
erly correlated with the probable needs of the crop and the 
soil, will determine whether a particular brand should be pur- 
chased or not. The real question here is not so much the 
actual quantities of the elements in a ton of the fertilizer, 
as it is their balance among themselves. The actual pounds of 
nitrogen, phosphoric acid, or potash applied to the acre can 
be governed by the rate at which the mixture is added. 

The purchase of high-grade goods is the second important 
point to be considered. Data collected from practically every 
State show that the higher the grade of the fertilizer, both as 
to availability and as to the percentage of the constituents 
carried, the greater is the amount of nutrients obtained for 
every dollar expended. Avoiding the abnormal war 
prices, the following data from Vermont ^ for 1909 seem 
representative : 

Table XCVIII 





Cost (in Cents) of One Pound of 


Cents' Worth 
OF Nutrients 


Mixed Fertilizer 


NH, P,0, 

i 


K,0 


Eeceived fob 

Every Dollar 

Expended 


Low grade 


32 
26 
23 


7.6 
6.3 
5.7 


8.5 
7.0 
6.3 


50 


Medium grade 

High grade 


60 
67 







^ Hills, J. L., Jones, C. H., and Miner, H. L., Commercial Fertilizers; 
Vt. Agr. Exp. Sta., Bui. 143, pp. 147-149, 1909. 



484 NATURE AND PROPERTIES OF SOILS 

It is always true that the lower the grade of a fertilizer the 
higher is the proportional cost of placing the goods on the 
market. In other words, it costs just as much a ton to market 
a low-grade material as a high-grade one. This accounts for 
the fact that the nutrients are cheaper a pound in a high- 
grade mixture, and that the value received for every dollar 
expended is greater. 

273. The purchase of unmixed fertilizers. — There has 
always been a tendency among fertilizer manufacturers to 
discourage the purchase by the farmer of the separate car- 
riers of fertilizer nutrients. When this was possible the fer- 
tilizer manufacturer was able absolutely to control the mar- 
ket. By selling only mixed goods the manufacturer could 
not only realize a profit on the ingredients themselves but a 
profit on the mixing in addition. In order to escape these 
costs many farmers have begun the practice of buying the 
separate carriers, thus avoiding the extra charges. In manjr^ 
cases, the mixing on the farm costs nothing, as it can be done 
in winter when the farm work is not pressing. Home-mixing 
has been greatly encouraged by post-war conditions. In 1920 
from ten to twenty dollars a ton was often saved on a high- 
grade mixture by purchasing the carriers separately. 

In many instances the fertilizing materials purchased sepa- 
rately need not be mixed at all, thus effecting a considerable 
saving in time and labor. Acid phosphate is generally added 
separately, especially to fall wheat. Bone-meal, basic slag, 
and raw rock give excellent results when applied with farm 
manure. Sodium nitrate and ammonium sulfate give good 
returns as a top dressing on meadows, pastures, and small 
cereals, especially if phosphates have been added at some 
other point in the rotation. When farm manure is available, 
the use of acid phosphate with lime and manure in a legume 
rotation is generally desirable. Even where little manure 
is available, the application of sodium nitrate or ammonium 
sulfate as a top dressing for meadows, with acid phosphate in 



THE PRINCIPLES OF FERTILIZER PRACTICE 485 

its proper place, is feasible. The purchase of expensive ready- 
mixed fertilizers may thus be avoided without necessitating 
home-mixing. 

For vegetable crops, however, especially potatoes, a com- 
plete fertilizer is generally advisable. Home-mixing is in such 
cases necessary. Special soils often demand a complete mix- 
ture. Muck soils generally require both potash and phos- 
phoric acid, while sandy soils, especially if the organic matter 
is low, respond to a mixture carrying all three of the fer- 
tilizer elements. 

As might be expected, this practice of home-mixing has met 
with much opposition from manufacturers. In general, it is 
claimed that the factory goods are more finely ground than 
those mixed by the farmer, and consequently the ready-mixed 
goods are not only more uniform but also in better physical 
condition. Also, the manufacturer is able to treat certain 
materials with acids, and thus increase their availability. 
While these reasons are more or less valid, good results may 
be expected from a fertilizer even though it may not be quite 
uniform, as the soil tends to equalize this deficiency. More- 
over, by screening and by using a proper filler, a farmer can 
obtain a physical condition which will in no way interfere 
with the drilling of the material. While, obviously, one farm- 
er alone cannot afford to buy small lots direct from the whole- . 
sale dealer because of the high freight charges, this objection 
is being met by organizations of various kinds whereby the 
single carriers may be purchased in carload lots and shipped 
directly to the association. 

It is evident that by purchasing the separate carriers, a 
farmer is able to obtain pure high-grade material at a reason- 
able price. Even if the fertilizers are not home-mixed, an 
educational value enters. The farmer is forced to study the 
influence of the materials on his crops more closely and is thus 
placed in a position to make changes that will tend to a higher 
efficiency of the constituents. The chances are that he will 



486 NATURE AND PROPERTIES OF SOILS 

advantageously alter his fertilizer practice as the rotation 
progresses and his soil changes in fertility. 

Such arguments do not always mean, however, that it pays 
to buy the separate materials. As a matter of fact, in many 
cases it does not pay, especially where only a small amount of 
fertilizer is needed and it is impossible to cooperate with 
other farmers. As a general rule, fertilizers should be bought 
by the method that will give the greatest value for every dollar 
expended, providing, of course, that the proper material is 
purchased. Farmers can often avail themselves of the advan- 
tage of both systems by asking for bids from various manu- 
facturers on carload lots of mixed goods having a certain 
composition. The farmers in this case designate the carriers 
as well as the formula. All the advantages of machinery mix- 
ing may thus be gained. 

274. How to mix fertilizers.^ — The first step in the buy- 
ing of the separate fertilizer carriers is to obtain quotations 
which should state the price a ton, the composition, and the 
freight rate. With this information, the most desirable car- 
riers are selected and the amount of each is calculated.^ If 

^ Certain materials should not be mixed, especially in large amounts. 
Thus lime, especially the oxide and hydroxide forms or fertilizers carry- 
ing lime in considerable amount, should not be mixed with ammonium 
sulfate and animal manures, since ammonia is likely to be freed. Such 
materials should be kept away from acid phosphate or the reversion of 
the latter will occur. Calcium carbonate in small amounts, however, is 
often mixed with fertilizers carrying acid phosphate. It is not wise to 
allow moist acid phosphate to lie in contact with sodium nitrate, as nitric 
acid may be liberated by free sulfuric acid. 
^ Below are three satisfactory mixtures : 
2-12-0 

400 pounds of tankage. 
100 pounds of sodium nitrate. 
1500 pounds of acid phosphate (16%P205). 
2-12-2 

320 pounds of tankage. 
100 pounds of ammonium sulfate. 
1500 pounds of acid phosphate (16%P206). 
80 pounds of potassium chloride. 
4-10-4 

150 pounds of sodium nitrate. 
100 pounds of ammonium sulfate. 



THE PRINCIPLES OF FERTILIZER PRACTICE 487 

the materials are to be applied separately, the rate to the acre 
and the number of acres must be known. If a mixture is to be 
made, the formula of this mixture must be decided on in addi- 
tion. The pounds of the various carriers necessary to produce 
a given amount of a certain mixture can now be calculated. 
All of this is a matter of good judgement and careful arith- 
metic.^ 

With the separate carriers at hand, the mixing, if necessary, 
is quickly accomplished. All that is needed may be listed 
as follows: (1) a tight floor, (2) a coarse sand screen, (3) a 
tamper or grinder, and (4) shovels, a rake, and like tools. 
Since the pounds of fertilizer are quoted on each bag, weigh- 
ing is unnecessary in making up a given amount of a mixture 
having a certain formula. Bags may be divided into half or 
quartered with sufficient accuracy. 

The bulkiest material is spread on the floor first and leveled 
uniformly by raking. The remaining ingredients are then 
spread in thin layers above the first, in the order of their bulk. 
Beginning at one side, the material is next shoveled over, care 
being taken that the shovel reaches the bottom of the pile each 
time. The pile is then again leveled, and the process is re- 
peated a sufficient number of times to insure thorough mixing. 
Sometimes a mixing machine may be used for this operation. 
For storage and general convenience, the fertilizer may be 
weighed into sacks of 100 to 150 pounds capacity and put in a 

240 pounds of tankage. 
100 pounds of dried blood. 
1250 pounds of acid phosphate (16%P205). 
160 pounds of muriate of potash. 

^ A 2-8-2 fertilizer is to be compounded from dried blood containing 
12% NH3, acid phosphate carrying 14% P2O5 and kainit containing 
12% K2O. In one ton of the mixture there should be 40 pounds of NH3, 
160 pounds of P2O5, and 40 pounds of K,0. 

40 H- .12 = 333 lbs. of dried blood. 
160^.14=1142 lbs. of acid phosphate. 
40 — .12= 333 lbs. of kainit. 
192 lbs. of filler. 

2000 lbs. total. 



488 NATURE AND PROPERTIES OF SOILS 

dry place until needed. Each sack should be labeled, especi- 
ally if different mixtures are made. 

A word of caution should be inserted here regarding the 
concentration of the mixture. Some farmers, in order to les- 
sen the work of mixing and application in the field, raise the 
percentage of the elements exceedingly high — a condition very 
likely to occur when high-grade materials are used. This 
sometimes is bad practice, in that it may interfere with ger- 
mination after the fertilizer is applied and may also injure 
the young plants. Also, it is likely to result in a poor physi- 
cal condition, which may clog the drill, and in uneven distribu- 
tion, which will bring about a lowered efficiency of the fertil- 
izer. The use of sufficient dry finely divided filler will obviate 
such dangers.^ 

275. The choice of a fertilizer. — Two primary considera- 
tions must be observed in the actual utilization of fertilizers. 
The first of these has to do with the composition of the fer- 
tilizer and its suitability to soil and to crop. A careful study 
should be made not only of the percentages of ammonia, phos- 
phoric acid, and potash but also the availability of these con- 
stituents. The second consideration in the rational use of 
fertilizing materials is in regard to the amounts to be applied. 
As much care and good judgment are necessary in handling 
a single carrier as a complete ready-mixed material, especially 
if the rotation as a whole is considered. 

It is evident, due to many factors that cannot be controlled, 
that fertilizer formulae for different crops on particular soils 
are difficult to determine. In fact, such data can never be 
more than merely suggestive. Further, the best quantity of a 
mixture to apply, even though it is perfectly balanced, is a 
figure that can only be approximated. Probably the largest 
percentage of the fertilizer waste that occurs annually can 

^Sand, dry soil, saw dust, dry muck, and even ground limestone, if in 
small amounts, may be used as fillers. 



THE PRINCIPLP^S OF FERTILIZER PRACTICE 489 

be charged to this factor. Many farmers make the mistake of 
applying too much fertilizer. Any information along such 
lines, however, can only be suggestive, rather than literal, 
it being understood that the general formula suitable to vari- 
ous crops, and the quantities ordinarily applied, are subject 
to wide variations. 

276. Fertilizer formulae.^ — In the popular mind, the nu- 
trition of a plant is considered as similar to and as easy as 
the proper feeding of an animal. With animals, the food is 
compounded with the correct balance of nutrients and if other 
conditions are favorable, normal results should be obtained. 
The nutrition of a plant is by no means as simple as the proper 
feeding of an animal. In the first place, the plant receives 
most of its nutrients from the soil and air and not from the 
fertilizer, since the latter usually merely supplements the nu- 
trients already present in the soil. Again, the food for the 
animal remains balanced as it is utilized. In the case of plants, 
the fertilizer nutrients undergo great changes on addition to 
the soil, the soil influencing the availability of the fertilizer 
as well as the fertilizer influencing the soil in a great number 
of different ways. Moreover, the question of fertilizer resi- 
dues, especially those of an acid nature, is always paramount 
when fertilizers are used over long periods. The proper for- 
mula for a given crop and a given soil under a probable series 
of weather conditions is thus more or less of a guess and will 
always remain so. 

^ The following example of fertilizers similarly named but carrying 
strikingly different guarantees are taken from Bull. 206 of the Vt. 
Agr. Exp. Sta. 

Potatoes and Maize Potatoes and Tobacco 

4-7-8 2- 6-7 

4-8-4 2- 6-4 

4-8-0 2-12-0 

Vegetables Top Dressings 

3- 7-10 7-6-5 

4- 8- 4 7-6-2 
5-10- 7-6-0 



490 NATURE AND PROPERTIES OF SOILS 

In spite of the intangible nature of the question, certain gen- 
eral rules seem to govern the compounding and use of fertiliz- 
ers. In the first place, the ratio of the nutrients removed by 
the average crop bears no relation to the composition of the 
fertilizer usually added. This is to be expected because of 
the complex changes that the fertilizer undergoes in the soil 
and because the different nutrients influence the plant di- 
versely. 

Table XCIX 





Eatio of the 


Eatio of the 




Constituents 


Constituents 


Constituents 


AS They Occur 


Carried by the 




in the Average 


Average 




Crop 


Fertilizer 


Ammonia 


4 
2 


0^2 


Phosphoric acid 


16-8 


Potash 


3 


(V-2 







It is immediately noticeable that the ratios of the ammonia 
and potash in fertilizers are low. The ammonia ratio is low 
because of the ready response of plants to nitrogen and the 
ease with which this constituent is lost from the soil. The 
potash ratio is likewise small because potassium is a rather 
expensive constituent and it is generally better if possible to 
render available by suitable means that which is already in 
the soil than to buy it commercially. The phosphoric acid 
is high in comparison with the ammonia and potash because 
of its complex reversion in the soil and the tendency of much 
of it to remain unavailable for long periods due to the high 
absorptive power of the soil. 

The following data may now be presented. These for- 
mulae are tentative and suggestive only, being a modification 
and curtailment of certain analyses standardized for the use 
of fertilizer manufacturers in the United States. 



THE PRINCIPLI^IS OF FERTILIZER PRACTICE 491 



Table C 
group i : fodder and staple crops. 
Wheat (fall) Maize Millet 

Oats Barley Beans (field) 

Rye (fall) Buckwheat Peas (field) 



Soil 


Without 
Farm Manure 


With 
Farm Manure 


Sandy soil 


2-10-6 

2-10-4 

J 2-12-2 

I 2-12-0 


0-12-4 I or Acid 
0-12-2 j Phos. 

Acid Phosphate 


Loamy soil 

Clayey soil 



Table CI 

GROUP II : TOP DRESSINGS. 



Soil 


Timothy, 
Orchard Sod 

and 
Meadows * 


Wheat, Eye 

AND Oats 

for Hay 

(Spring 

Dressing)* 


Pastures* 

AND 

Legumes 


Sandy soil 

Loamy soil 

Clayey soil 


7-8-6 

7-8-3 
7-8-0 


7-8-3 
7-8-0 
7-8-0 


0-10-8] %;^^^^^ 

0-12-4 P^«^: 
f. ,r, 9 for Basic 

"■-^^-^J Slag 



* Note. — Sodium nitrate or ammonium sulfate may be used alone as 
a top-dressing on all of these crops except legumes. 



Table CII 
group iii: vegetables. 



1. Extensively — Tomatoes, 
sweet corn, beets, cab- 
bage, etc. 

Sandy soil 3-10-6 

Loamv soil 3-10-4 

3-10-2 
■10-0 

All root-crops should re- 
ceive at least 2 per cent, 
of K,0. 



Clayey soil jg 



2. Intensively — Cabbage, let- 
tuce, celery, asparagus, 
etc. 

Sandy soil 4-10-6 

Loamy soil 4-10-4 

Clayey soil 4-10-2 

The ammonia should be re- 
duced if farm manure is 
used. 



492 NATURE AND PROPERTIES OF SOILS 

3. Miscellaneous. 

rSandy soil 7-6-5 

a. Early potatoes * ■< Loamy soil 5-8-5 

[clayey soil 4-8-4 

rSandy soil 5-8-7 

b. Late potatoes * J Loamy soil 4-8-6 

[clayey soil 4-8-4 

c. General trucking * on sandy soils of Atlantic 

seaboard 5-8-7 

* Note. — Eeduce ammonia if farm manure is used. 

In this table of suggested formulae, it is noticeable that 
wberever manure is used, the ammonia is reduced or even 
eliminated. Ammonia is also unnecessary on leguminous 
crops. With vegetables, the ammonia is usually high. Top 
dressings for pastures, meadows, and cereals in the spring 
should always carry large quantities of readily available nitro- 
gen. 

In a mixed fertilizer, the phosphoric acid is generally high, 
for reasons already explained. Due to the absorptive power 
of a clay, the mixture applied to such a soil should generally 
carry more phosphorus than that added to a sandy soil. Pot- 
ash is usually lower in a fertilizer for clayey soils, due to the 
possibility of liberating potassium from the soil itself by good 
soil management. 

277. Amounts of fertilizers to apply. — The agricultural 
value of a fertilizer is necessarily a variable quantity, since, 
in applying fertilizers, a material subject to change is placed 
in contact with two wide variables, the soil and the crop. 
Moreover, soil conditions are constantly changing, thus forc- 
ing a modification of the fertilizer applied to the same soil 
bearing the same crop at different times. The factors influ- 
encing the efficiency of a fertilizer application may be listed 
as follows : (1) seed, crop, and adaptation of crop, (2) weather 
conditions, (3) physical condition of the soil, including drain- 



THE PRINCIPLES OP FERTILIZER PRACTICE 493 

age, (4) organic content of the soil, and (5) chemical constitu- 
tion of the soil and its reaction. 

Although the conditions affecting fertilizer efficiency have 
thus been so briefly disposed of, it is evident that they are of 
vital importance in the economical utilization of fertilizing 
materials. One point of broader scope stands out particularly 
in this connection — the necessity of putting a soil in any 
given climate in the best possible condition for plant growth. 
This means that drainage, lime, organic matter, and tillage, 
in the order named, must be raised to their highest perfection 
in order to realize the best results from fertilizers. 

Such considerations indicate that the decision as to the 
amount of a single carrier or of a mixed fertilizer that should 
be applied will be difficult and probably more indefinite than 
formula selection. In fact, the amount of a fertilizer applied 
to the acre is more vital than the actual chemical composition, 
as far as money returns are concerned. 

With all the groups considered above, except garden and 
root-crops, the applications are generally relatively light, rang- 
ing from 150 to 350 pounds to an acre. Where excessive vege- 
tative growth is required, as in silage, the rate may be in- 
creased to 500 pounds. In the top dressings of meadows or 
grains, the rate varies from 100 to 200 pounds an acre. Very 
often this dressing is sodium nitrate or ammonium sulfate 
alone. With garden and root-crops, the amount of fertilizer 
applied is very large, ranging from 800 to sometimes as high 
as 2000 pounds. The cropping here is intensive, and the ex- 
penditure for fertilization may be large and yet yield substan- 
tial profits. 

278. The law of diminishing returns. — It must always 
be remembered that in fertilizer practice the very high yields 
obtained under fertilizer stimulation are not always the ones 
that give the best returns on the money invested. In other 
words, the law of diminishing returns is a factor in the in- 
fluence of fertilization on crop yield. After a certain point 



494 NATURE AND PROPERTIES OF SOILS 

is reached, the return for each added increment of fertilizer 
becomes less and less. It is evident, therefore, that with an 
excessive application of any mixture, the returns to an in- 
crement will at last become so small that the increased crop 
fails entirely to pay for even the fertilizer, not to mention 



IS 




























• 


— 


— ■ 


/ 


^ 






















{ 




























■JO 


sc 


o 


IZ 


dd 


/bOO 


zooo 


Z4C0 



POUmS OF FL0AT3 yiPPLIED PEiR. ^CRE 




4X10 aoO /200 /600 2000 

POUnOS OF FLOATS APPLIED PER /JC/ZEl 



£400 



Fig. 60. — In the upper diagram the heavy line indicates the increase 
in the yield of maize due to graduated applications of floats. The 
lower diagram shows how the cost of the fertilizer approaches and 
finally exceeds the value of the crop as the applications increase 



such charges as cost of application, harvesting of increased 
crop, storage, and the like. The application of moderate 
amounts of fertilizer is to be urged for all soils until the maxi- 
mum paying quantity that may be applied to any given crop 
is ascertained by careful experimentation. Over-fertilization 
probably accounts for the fact that such a large proportion of 



THE PRINCIPLES OF FERTILIZER PRACTICE 495 

the fertilizer sold to farmers each year not only is entirely 
wasted, but probably in some cases even becomes detrimental 
to crop yield. 

The law of diminishing returns may be illustrated by data 
from the Cornell University Agricultural Experiment ^ Sta- 
tion. Floats were applied at different rates to plats receiv- 
ing a uniform dressing of farm manure at the rate of 15 
tons to the acre. Table CIII shows the increased yields of 
maize due to the treatment with the rock phosphate. Pre- 
war prices were used in the calculations. (See Fig. 60.) 

Table CIII 



Pounds of Floats 
TO THE Acre 


Maize 
(bus.) 


Maize 

(VALUE) 


Floats 
(cost) 


Difference 


200 


7.0 

8.3 

10.2 

12.7 


$4.62 
5.48 
6.73 

8.38 


$ .90 

1.80 

3.60 

10.80 


+$3.72 
+ 3.68 
+ 3.13 
— 2.42 


400 


800 


2400 







279. Method and time of applying fertilizers. — 
Although considerable emphasis has been placed on the selec- 
tion of the correct fertilizer formulae and on the adequate and 
economical amounts to use, the method of application must 
not be lost sight of. A fertilizer is never effective unless uni- 
formly distributed. It should also be placed in the soil in 
such a position that it will stimulate the plant to the best 
advantage. 

The distribution of the fertilizer by means of machinery 
is much more satisfactory than is broadcasting by hand, 
as the former method gives a more uniform distribution. 
Cereals and other crops are now usually planted with a drill 
or a planter provided with an attachment for dropping the 
fertilizer at the same time that the seed is sown, the fertilizer 

'Lyon, T. L., Soils arid Fertilizers; p. 216; New York, 1917. 



496 NATURE AND PROPERTIES OF SOILS 

being by this method placed under the surface of the soil. 
Broadcasting machines are also used, which leave the fer- 
tilizer uniformly distributed on the surface of the ground, 
permitting it to be harrowed in sufficiently before the seed is 
planted, thus preventing injury to the seed by the chemical 
activity of the fertilizing material. 

Corn-planters with fertilizer attachments deposit the fer- 
tilizer beneath the seed, thus avoiding a possible detrimental 
contact. Grain-drills do not do this, and, where the amount 
of fertilizer used exceeds 300 or 400 pounds an acre, it is 
better to apply it before seeding. Grass and other small seeds 
should be planted only after the fertilizer has been mixed 
with the soil for several days. For crops to which large quan- 
tities of fertilizers are to be added, especially potatoes and 
garden crops, it is desirable to drop only a portion of the 
fertilizer with the seed, the remainder having been broad- 
casted by machinery and harrowed in earlier. 

280. Systems of fertilization. — During the evolution of 
fertilizer practice since the middle of the nineteenth century, 
a number of systems of applying fertilizers have been advo- 
cated and in many cases actually followed. Perhaps the first 
plan to be suggested was the single element system. At that 
time, each crop was supposed to respond largely to one par- 
ticular element. Thus, nitrogen was supposed to dominate 
wheat, rye, and oats; phosphoric acid, to dominate maize, 
turnips, and sorghum; and potash to dominate potatoes, 
clover, and beans. Present knowledge of plant nutrition and 
the balancing effects of fertilizer nutrients show this idea to 
be fallacious. 

The supplying of abundant minerals as a fertilizer system 
had its origin from the fact that potash and phosphoric acid 
are relatively cheap and are rather slowly leached from the 
soil, while nitrogen is expensive and easily lost in this way. 
Such a plan, therefore, always provides plenty of potash and 
phosphoric acid, which are to be balanced each season with 



THE PRINCIPLES OF FERTILIZER PRACTICE 497 

sufficient nitrogen to give paying yields. While this system 
is not feasible in its entirety at the present time, the prin- 
ciple involved is worthy of incorporation with more economi- 
cal plans. 

A system based on the amount of nutrients removed by 
crops has received from time to time considerable support. 
According to this plan, as much plant-food material is added 
each year as will probably be taken out by the plant, this 
being determined by chemical analyses of the crop. The 
system not only overlooks the fact that diverse plants feed 
differently on the same soil, but that the same crop exhibits 
marked variability with change of season and change of soil. 
]\Ioreover, no allowance is made for losses by leaching, which 
are known to equal at times the losses due to plant absorption. 

In trucking or in general farming operations, one crop is 
often the money crop. Naturally its stimulation by heavy 
fertilization will pay better than applications to crops that 
bring less on the market. The general plan in this system 
is to allow the crops following the money crop to utilize 
the residuum. When this residual influence works out fa- 
vorably, the system is likely to be a profitable one; but when 
the following crops fail to respond, the method becomes 
wasteful in the extreme. 

281. Rational fertilizer practice. — In the selection of a 
system that will result in an effective utilization of fertilizers, 
only two of the plans described above need be considered. In 
any fertilizer, phosphoric acid and usually potash should 
always be present in amounts sufficient more than to balance 
the nitrogen, since the activity of nitrogen is so pronounced. 
Therefore, a scheme that calls for an abundance of minerals 
is a sound one. This, coupled with the heavy fertilization 
of the money crop, does not, however, constitute what might 
be considered a rational system, since the crops that follow 
may or may not be adequately supplied with nutrients. 

Not only must the soil, the crop and the fertilizer formula 



498 NATURE AND PROPERTIES OF SOILS 

and amount receive careful study, but the rotation should 
be considered in addition. This is a fundamental principle 
not only with the application of commercial fertilizers but 
with liming and the use of farm manure as well. The care- 
ful fertilization of the rotation, with special reference to the 
money crop, is the only rational system that should ordi- 
narily be employed, since it not only cares for the crop on the 
land but also looks to those that are to follow. The atten- 
tion that must necessarily be paid to the fertility of the soil 
in such a system insures the establishment of a soil manage- 
ment which will result in an economical use of the plant 
nutrients, while at the same time the yields will be raised and 
a continuous productivity will be provided for. 



CHAPTER XXIV 
FARM MANURE ^ 

Of all the by-products of the farm, barnyard manure is 
probably the most important, since it affords a means where- 
by the unused portion of the crop may become a part of 
the soil. Its use not only makes possible a return to the 
land of a part of the nutrients previously removed by the 
crop but also permits an actual gain of carbohydrate ma- 
terials, the elements of which the plant obtains not from 
the soil but from air and water. 

This country has already entered an era in which the pre- 
vention of agricultural waste is becoming necessary and a 
nearer approach to a self-sustaining system of soil manage- 
ment more and more essential. For the maintenance of fertil- 
ity, a careful handling and a wise utilization of all the manure 

* The following publications will be valuable : 

Ames, J. W., and Gaither, E. W., Barnyard Manure; Ohio Agr. Exp. 
Sta., Bui. 246, June 1912. 

Hart, E. B., Getting the Most Profit from Farm Manure; Wis. Agr. 
Exp. Sta., Bui. 221, June 1912. 

Thome, C. E., Farm Manures; New York, 1914. 

Beavers, J. C, Farm Manures; Purdue Univ. Agr. Exp. Sta., Cire. 49, 
Mar. 1915. 

Burdick, R. T., Concerning Farm Manures; Vt. Agr. Exp. Sta., Bui. 
206, June 1917. 

Fippin, E. O., Farm Manure; Cornell Eeading Course for the Farm, 
Lesson 127, Aug. 1917. 

Weaver, F. P., Far7yi Manure; Pa. State Coll., Ext. Circ. No. 67, Oct. 
1917. 

Brodie, D. A., Handling Barnyard Manure in Eastern Pennsylvania; 
U. S. Dept. Agr., Farmers' Bui. 978, July, 1918. 

Wiancko, A. T., and Jones, S. C, The Value of Manure on Indiana 
Soils; Purdue Univ. Agr. Exp. Sta., Bui, 222, Sept. 1918. 

Duley, F. !<., Handling of Farm Manure; Mo. Agr. Exp» Sta., Bui. 
166, Sept. 1919. 

499 



500 NATURE AND PROPERTIES OF SOILS 

produced on the farm are vital. Obviously an understanding 
is necessary regarding the character and composition of farm 
manure, its fermentative and putrefactive changes, its losses 
in handling and storage, and above all its rational use as an 
amendment and a fertilizer. This need appeals not only to 
the wide-awake farmer but to the technical man as well, since 
in the use of farm manures theory and practice widely over- 
lap. 

282. Composition and general characteristics of farm 
manures. — The term farm manure may be employed in ref- 
erence to the refuse from all animals of the farm, although, 
as a general rule, the bulk of the ordinary manure which 
ultimately finds its way back to the land is produced by 
cattle and horses. This arises because these animals consume 
the greater part of the grain and roughage on the average 
farm, and because the methods of handling such live-stock 
make it easier and more practicable to conserve their excreta. 
Yard manure generally refers to mixed manures. The mixing 
usually occurs during storage, either for convenience in han- 
dling or for the purpose of checking losses and facilitating 
fermentation. Thus, horse and cow manures are commonly 
mixed, since the too rapid putrefaction and consequent loss 
of ammonia in the former is checked, while at the same time 
a more rapid and much more complete decomposition is en- 
couraged in the latter. 

Ordinary manure consists of two original components, 
the solid, or dung, and the urine in about the rate of three 
to one. As these constituents differ greatly, not only in com- 
position but also in physical properties, their proportions 
must appreciably affect the quality of the excreta and its agri- 
cultural value. Litter added for bedding or for absorptive 
purposes is almost always an important factor, for while it 
prevents losses of the soluble constituents, it may at the same 
time lower the value of the product for a unit amount. 

While compilations of available data on the composition of 



FARM MANURE 



501 



farm manures demand liberal interpretations, they afford 
considerable light regarding the dififerences to be expected be- 
tween excrement from various animals. 

Table CIV 

THE COMPOSITION OF FRESH MANURE.^ 





Percentage of 




H^O 


NH3 


P.0« 


KjO 


Solid, 80% 

Horse j Urine, 20% 

Whole manure .... 

'Solid, 70% 

Cow purine, 30% 

Whole manure .... 

Solid, 67% 

Sheep j Urine, 33% 

^Whole manure 

[Solid, 60% 

Swine I Urine, 40% 

Whole manure 


75 
90 
78 

85 
92 
86 

60 

85 
68 

!80 
97 

87 


.66 
1.63 

.84 

.48 

1.21 

.72 

.90 
1.63 
1.14 

.66 

.48 
.60 


.30 

Trace 

.25 

.20 

Trace 

.15 

.50 
.05 
.35 

.50 
.10 
.35 


.40 

1.25 

.55 

.10 

1.35 

.45 

.45 
2.10 
1.00 

.40 
.45 
.40 



Since the horse does not ruminate its food, the manure is 
likely to be of an open character. It is also fairly dry, as is 
that from sheep, the urine in these two manures making up 
20 and 33 per cent., respectively, of the whole product. The 
complete manure from these two animals contains 78 and 
68 per cent., respectively, of water — a considerable contrast 
to the cattle and swine increments. Cattle and swine ma- 
nures, being very wet, are rather solid and compact. The air, 
therefore, is likely to be excluded to a large degree and de- 
composition is relatively slow. They are usually spoken of 
as cold inert manures as compared with the dry, open, rapidly 
heating excrements obtained from the horse and the sheep. 

*Van Slyke, L. L., Fertilizers and Crops, p. 291; New York, 1912. 



502 NATURE AND PROPERTIES OF SOILS 



In every case except that of swine, the urine is much the 
richer than the dung in ammonia, containing on an average 
more than twice as much when compared on the percentage 
basis. The urine is also richer in potash than the solid, aver- 
aging for the four classes of animals 1.29 per cent, as com- 
pared to 0.34 per cent, contained in the solid manure. Most 
of the phosphoric acid, however, is contained in the solid ex- 



Z&7>?Z. 


TOTAL 


TOTOL 


/^MMON/A 


PAy03P/V0^/C 


F>OT^3/-/ 


o.e% 


P)C/D 


c>.s%- 



S5% 




65% 



45% 



/oo% 



35% 



T^AC£ 



Diy/VG. u^//v£:. 



PUNG. u/e/r^E. 



PUNG. lAe/A/fT. 



Fig. 61. — Diagram showing the distribution of ammonia, phosphoric 
acid and potash between the dung and urine of average farm 
manure. 

crement, only traces being found in the urine except in the 
case of swine. It is, therefore, evident that the urine, pound 
for pound, is more valuable insofar as the nutrient elements 
are concerned. The advantage leans heavily toward the 
urine also in that the constituents therein contained are im- 
mediately available ; this cannot be said of the solid manure. 
283. Liquid versus solid manure. — While the urine car- 
ries more nutrients to an equal weight than the dung, it yet 
remains to be seen whether in the total excreta voided by an 
animal there are more nutrients in the urine than in the dung. 



FARM MANURE 



503 



In general, more solid manure is excreted than liquid, tend- 
ing to throw the advantage toward the former as a carrier 
of plant nutrients. The following table, adopted from Van 
Slyke,^ bears on this point : 

Table CV 

distribution of nutrient constituents between the liquid 
and the solid of whole manure. 



Animal 


Percentage 

OP Total 

NH3 


Percentage 

OF Total 

P.O. 


Percentage 
OF Total 




SOLID 


LIQUID 


SOLID 


LIQUID 


SOLID 


LIQUID 


Horse 


62 
49 
52 
67 


38 
51 
48 
33 


100 

100 

95 

88 





5 
12 


56 
15 
30 
57 


44 


Cow 

Sheep 

Swine 


85 
70 
43 






Average 


57 
55 


43 
45 


95 
100 


5 



40 
35 


60 


Average for horse and cow 


65 



It is seen here that a little more than one-half the am- 
monia, almost all the phosphoric acid, and about two-fifths 
of the potash, are found in the solid manure. Nevertheless, 
this apparent advantage of the solid manure is balanced by 
the ready availability of the constituents carried by the urine, 
giving it in total about an equal commercial and agricultural 
value with the solid excrement. Such figures are suggestive 
of the care that should be taken of the liquid manure. Its 
ready loss of ammonia by fermentation and putrefaction, and 
the ease with which all its valuable constituents may escape 
by leaching, should make it an object of especial regard in 
handling. (See Fig. 61.) 

284. Poultry manure. — While poultry manure is often 
produced on the farm in large quantities, it is not included 
under the term farm manure, which, as generally used, refers 

'Van Slyke, L. L., Fertilizers and Crops, p. 295; New York, 1912. 



504 NATURE AND PROPERTIES OF SOILS 



to the excrement of the larger animals. Its general composi- 
tion is as below, the data being averages from Thorne.^ 

Table CVI 
composition of poultry manure. 



■ Condition 


Percentage of 


H,0 


NH3 


P.O. 


K2O 


Whole manure, fresh 

Whole manure, air dry 


57 

7 


1.31 

2.84 


.40 
.86 


.50 
1.08 



It is to be seen that poultry manure in the air-dry state, 
the condition in which it is applied, has over twice the 
amounts of nutrients carried by the other classes. It should 
be applied to the soil at at least one-half the rate commonly 
recommended for ordinary farm manure. Notwithstanding 
its ease in handling and its great value, poultry manure re- 
ceives less care and attention than any other produced on the 
farm. 

285. Farm manure — a direct and indirect fertilizer. — 
Farm manure, when applied to the land, ordinarily fulfills 
two functions which are usually not so distinctly developed in 
one material — that of a direct and indirect fertilizer. Mixed 
farm manure ready to apply to the land contains on the aver- 
age .6 per cent, of ammonia, .25 per cent, of phosphoric acid 
and .5 per cent, potash.- It is obviously a low-grade fertilizer 

^ Thome, C. E., Farm Manures, p. 90; New York, 1914, Also, 

Storer, F. H., Agriculture, Vol. I, p. 613; New York, 1910. 

Vorhees, E. B., Ground Bone and Miscellaneous Samples; N. J. Agr. 
Exp. Sta., Bui. 84, 1891. 

Goessman, C. A., Mass. Agr. Exp. Sta., Bui. 37, 1890, and Bui. 63, 
1896. 

*See Analyses, Storer, F. H., Agriculture, pp. 237-248; New York, 
1910. 

Thorne, C. E., Farm Manures, pp. 89-93; New York, 1914. 

Aikman, C. M., Manure and Manuring, pp. 279-292; Edinburgh and 
London, 1910. 

Roberts, I. P., The Fertility of the Land, pp. 159-182; New York, 
1904. 



FARM MANURE 505 

both as to the amounts of nutrients carried and as to their 
availability. Because of the large acre applications of ma- 
nure commonly made, the fertilizer constituents added in ma- 
nure are considerable. Ten tons of farm manure, even if only 
one-half its ammonia, one-sixth of its phosphoric acid and one- 
half of its potash were readily available, are equal in fertil- 
izing value to 333 pounds of sodium nitrate, 52 pounds of 
acid phosphate, and 416 pounds of kainit. This equiva- 
lent to the addition of 801 pounds of a readily available mix- 
ture of fertilizer salts. This calculation, however, ignores 
an equal quantity of nutrients which remain in the soil as 
a residuum and may be used by succeeding crops. This resi- 
dual effect of manure is generally a paying one during the 
period of an ordinary rotation. 

Farm manure acts as an indirect fertilizer in that it adds 
to the soil organic matter and thus improves the physical 
condition of the land. While it may not increase the organic 
matter of the soil, because of the loss of carbon by exhalation 
and leaching during the period of crop growth, its use materi- 
ally influences the rate of reduction. Better aeration, drain- 
age and bacterial activity ^ of necessity result from such an 
addition. The influence of manure on the availability of 
the mineral constituents of the soil is not the least of its 
indirect actions. The fact that rock phosphate when mixed 
with manure seems to have a higher availability bespeaks 
a considerable solvent activity. The tendency of farm 
manure to alleviate toxic conditions, such as alkali and acid- 
ity, deserves attention. 

286. Outstanding characteristics of farm manure. — As 
farm manure is essentially^ a fertilizer, whether it is pro- 
duced on the farm or purchased outright, it is logical to con- 
trast it with the ready-mixed materials on the market. In 

* Conn, H. J., and Bright, J. W., Ammonification of Manure in 
Soil; Jour. Agr. Res., Vol. XVI, No. 12, pp. 313-350, March, 1919. 

Fulmer, H. L., and Fred, E. B., Nitrogen Assimulating Organisms in 
Manure; Jour Bact., Vol. II, No. 4, pp. 423-434, 1917. 



506 NATURE AND PROPERTIES OF SOILS 

such a comparison, five characteristics are outstanding: (1) 
the moist condition of manure, (2) its low grade, (3) its 
unbalanced nutrient condition, (4) its variability, and (5) 
its rapid fermentative and putrefactive processes. These 
characteristics, neither present nor desirable in ordinary fer- 
tilizers, place farm manure in a class by itself as to its hand- 
ling, storage, and field utilization. 

Of the above points, the first three may be disposed of 
quickly. Average farm manure, whether fresh or well-rotted, 
contains from 70 to 85 per cent, water. A ton of average 
mixed manure when applied to the land carries but 12 pounds 
of ammonia, 5 pounds of phosphoric acid, and 10 pounds of 
potash to the ton. Approximately one-half, one-sixth, and 
one-half, respectively, of these constituents are readily avail- 
able. Farm manure is, therefore, low-grade on two distinct 
counts. Moreover, its readily available nutrients approximate 
a ratio of about 6-1-6, a marked contrast to the 2-8-2 often 
given for the average ready-mixed fertilizers on the market. 
Obviously, manure is much too low in phosphoric acid for its 
content of active ammonia and potash. The variability and 
decomposition of farm manure will be considered separately. 

287. Variability of farm manure. — The manure pro- 
duced on the average farm will obviously vary in its char- 
acter and composition from time to time. The factors re- 
sponsible may be listed as follows: (1) class of animal, (2) 
age, condition, and individuality of animal, (3) food, and 
(4) the handling and storage which the manure receives be- 
for it is placed on the soil. 

The differences in composition due to class of animal have 
been adequately disposed of in previous paragraphs. In ad- 
dition, it is obvious that the age and condition of any 
animal within a class will influence the character of the ex- 
crement produced. A young animal gaining in bone and 
muscle will retain large amounts of nutrients, and the manure 
will be correspondingly poorer in dry matter, nitrogen, lime, 



FARM MANURE 507 

phosphoric acid, and potasli. A fattened animal on a main- 
tenance ration will return almost all of the nutrient value of 
the original food. 

Since the animal will retain oidy a certain quantity of 
the important food elements, it is only reasonable to assume 
that the richer the food, the richer will be the corresponding 
excrement. The following data from Ohio ^ obtained with 
western lambs substantiate this assumption: 

Table CVII 
effect of ration on manurial composition. 

Percentage of 
Eation 




Corn and mix hay 

Corn, oil meal and hay 

Corn, oil meal and clover I 2.03 



While the factors just disposed of cause some variation in 
farm manure, the character of the product as it goes on to 
the land is determined in large degree by the handling. Tight 
floors and proper bedding hold the liquid manure in contact 
with the solid and thus maintain the proportion of valuable 
constituents. A neglect of these two conditions means a grave 
loss in value. The storage of manure, when it is not taken 
directly to the field, always results in loss not only of organic 
matter, but of ammonia and minerals as well. As more than 
one-half of the ammonia and potash are water-soluble, seri- 
ous loss is unavoidable. Such losses over-ride other causes of 
variation. The influence of storage is clearly shown by the 
following figures from Schutt ^ on mixed horse and cow 

^Thorne, C. E., and others. The Maintenance of Fertility; Ohio Agr. 
Exp. Sta., Bui. 183, 1907. 

^Sehntt, M. A., Barnyard Manure; Canadian Dept. Agr., Centr. Exp. 
Farm, Bui. 31, 1898, 



508 



NATURE AND PROPERTIES OF SOILS 



manure. The protected manure was stored in a bin under 
a shed. The exposed sample was in a similar bin but unpro- 
tected. 

Table CVIII 

loss of constituents from protected and unprotected 

MANURE. 



Constituents 


Percentage Loss at 
End of Six Months 


Percentage Loss at 
End of One Year 




PROTECTED 


EXPOSED 


PROTECTED 


EXPOSED 


Loss of organic matter 
Loss of NH, 


58 

19 



3 


65 
30 
12 

29 


60 

23 

4 

3 


69 
40 


Loss of PgOr; 

Loss of K.,0 


16 
36 







288. The fermentation and putrefaction of manure.^ — 

In the process of digestion, the food of animals becomes more 
or less decomposed. This condition comes about partly be- 
cause of the digestive process and partly from the bacterial 
action that takes place. Of these two influences within the 
animal, bacterial activities are probably of the greater im- 
portance as far as the breaking-up of the complicated food- 
stuffs is concerned. The fresh excrement, then, as it comes 
from the stable, consists of decayed or partially decayed 
plant materials, with a certain amount of broken-down animal 
tissue and mucus. This is more or less intimately mixed with 
litter and the whole mass is moistened with the liquid excre- 
ment carrying considerable quantities of soluble nitrogen and 
potash. This mass of material, ranging from the most com- 

^Good general discussions may be found as follows: Lipman, J. G., 
Bacteria in Relation to Country Life, pp. 303-3.56 ; New York, 1911. 

Hall, A. D., Manures and Fertilizers, pp. 184-210; New York, 1921. 

For a technical discussion see Russell, E. J., and Richards, E. H., The 
Changes Taking Place During the Storage of Farm Manure; Jour. Agr. 
Sci., Vol. VIII, Part 4, pp. 495-563, Dec, 1917, 



FARM MANURE 509 

plex compounds to the most simple, is teeming with bacteria,^ 
especially those that function in fermentatio)i and putrefac- 
tion. The number very often runs into billions to a gram 
of excrement. In such an environment, it is little wonder 
that biological changes go on rapidly. These changes may be 
grouped for convenience of discussion under two heads — 
aerobic and anaerobic. 

When manure is first produced, it is likely to be rather 
loose, and if allowed to dry at once it becomes well aerated. 
The first bacterial action is, therefore, likely to be rather 
largely aerobic in nature. Transformations are very rapid 
and are accompanied by considerable heat, ranging from 100° 
to 150° F. and sometimes higher. This action falls largely 
on the simple nitrogenous compounds, although the more 
complicated nitrogenous and non-nitrogenous constituents are 
by no means unaffected. Urea is particularly influenced by 
aerobic activities and quickly disappears from well-aerated 
manure. 

CON.H^ + 2H,0 = NHJ2CO3 
NHJ.COa = NH3 + CO, + H3O 

Thus nitrogen may be rapidly lost from manure by allow- 
ing excessive aerobic decay and decomposition to proceed. 
This loss, however, is often somewhat checked by the oxidiz- 
ing influence of nitrifying bacteria, especially in the outer 
portions of the manure pile. The evolution of carbon dioxide 
which goes on continuously indicates how extensively the 
organic matter of the manure is suffering through biological 
activity. 

As the manure becomes compacted, especially if it is left 

moist, oxygen is gradually excluded from the heap and its 

place is taken by carbon dioxide, which is given off during 

the progress of any form of bacterial activity. The decay 

now changes from aerobic to anaerobic, it becomes slower, and 

^Murray, T. J., Studii of the Bacteria of Fresh and Decomposing 
Manure; Va. Agr. Exp. Sta., Bui. 15, Part II, 1917. 



510 NATURE AND PROPERTIES OF SOILS 

the temperature falls to as low as 80° or 90° F. New organ- 
isms may now function, although many of those active under 
aerobic conditions may continue to be effective. The prod- 
ucts become changed to a considerable degree. Carbon diox- 
ide, of course, continues to be evolved in large amounts, but 
instead of ammonia being formed, the nitrogenous matter is 
converted into the usual putrefactive products, such as indol, 
skatol, and the like. If sufficient reduction occurs, free nitro- 
gen may escape. 

The carbonaceous matter is resolved into numerous hydro- 
carbons, of which methane (CH^) is prominent; and as a by- 
product of the breaking-down of the proteins, hydrogen sul- 
fide (HgS) and sulfur dioxide (SO2) are evolved. The com- 
plex nitrogenous and carbohydrate bodies are attacked with 
the splitting-off, not only of simpler materials, but often of 
those more complex. Such compounds may be listed in gen- 
eral as organic acids and humous bodies. They, of course, ul- 
timately succumb to simplification. 

The general changes ^ in any manure pile can readily be 
recapitulated. First is the aerobic action, with the escape of 
ammonia and carbon dioxide. Next the manure is wetted, 
it compacts, and the slow, deep-seated decay sets in with a 
simplification of some compounds, with the production of 
acids, and with a gradual formation of humous materials. 
As the manure becomes alternately wet and dry, the two gen- 
eral processes may follow each other in rapid succession, the 
anaerobic bacteria attacking the complex materials, the 
aerobic affecting both the complex and the simpler com- 

* The proteid compounds, which are the most important group in farm 
manures, split up in the soil or compost heap into amino-acids. These 
amino-acids undergo deaminisation and decarboxylation. The former 
takes place either under aerobic or anaerobic conditions producing am- 
monia and a complex acid. The decarboxylation occurs only when oxygen 
is excluded giving either ammonia and an organic acid as in deaminisa- 
tion, or carbon dioxide and a complex amine, which may be rather stable. 
Deaminisation and decarboxylation go on together, the former generally 
predominating. 



FARM MANURE 511 

pounds. Carbon dioxide is given off continuously during the 
process. Some gaseous nitrogen as well as ammonia is prob- 
ably lost because of the rai)id alternations of conditions.^ 

289. Effect of decomposition on the value of manure. — 
Because of the great loss of carbon dioxide and water dur- 
ing the decay processes, there is considerable change in bulk 
of the manure. Fresh excrement loses from 20 to 40 per cent, 
in bulk by partial rotting and 50 per cent, bj^ becoming more 
thoroughly decomposed. This means that 1000 pounds of 
fresh manure may be reduced to 800, 600, or 500 pounds, 
according to the degree of change it has undergone. 

It is often argued that if the manure is properly stored, 
this rapid loss of carbon dioxide and water will raise the 
percentage amounts of the fertilizer elements. The simplify- 
ing action of the anaerobic fermentation and putrefaction 
is an additional reason for expecting better results from well- 
rotted manure when it is compared, ton for ton, with the 
fresh material. In practice, however, the losses in handling 
due to leaching and fermentation are so dominant as to place 
well-rotted manure at a disadvantage except on sandy land or 
for garden and trucking purposes. At the Ohio Experiment 
Station,^ yard and stall manure were compared in equal 
amounts in a three-year rotation of maize, oats, and hay. The 
3'ard manure was exposed for some months in the open, while 
the stall manure came directly from the stable. The increase 
due to yard manure is taken as 100 in each case. (Table CIX, 
p. 512.) 

A change of a biological nature which sometimes takes 
place in loose and rather dry manure is fire-fanging. Many 
farmers consider this to be due to actual combustion, as the 

* Under the alternating ai-robic and anaerobic conditions found in the 
average manure pile, gaseous nitrogen seems to be lost in considerable 
amounts. This loss probably occurs through the oxidation of ammonia 
to nitrites or nitrates with a later reduction of the nitrogen so carried 
to a free state. 

- Thorne, C. E., The Maintenance of Fertility ; Ohio Agr. Exp. Sta., 
Bui. 183, p. 209, 1907. 



512 NATURE AND PROPERTIES OF SOILS 



Table CIX 
comparative yields prom yard and stall manure, 





Average Increase to the Acre 


Manure 


Corn, 10 Years 


Wheat, 10 Years 


Hay, 




grain 


STOVER 


GRAIN 


STOVER 


6 Years 


Stall 


100 

72 


100 
68 


100 
85 


100 

87 


100 


\ ard 


54 











manure is very light in weight and has every appearance of 
being burned. This condition, however, is produced by fungi 
instead of bacteria, and the dry and dusty appearance of the 
manure is due to the mycelium, which penetrates in all di- 
rections and uses up the valuable constituents. Manure thus 
affected is of little value either as a fertilizer or as a soil 
amendment. 

290. Evaluation of farm manure. — For purposes of com- 
parison, experimentation, and sale, farm manures are often 
evaluated in a way similar to that used with commercial fer- 
tilizers. The great difficulty here lies in arriving at prices 
for the important constituents which are at all comparable 
with the value of the manure in the field. If the value of the 
ammonia in manure is arbitrarily placed at 15 cents a pound, 
phosphoric acid at 5 cents, and potash at 8 cents, certain 
tentative calculations may be made. While such assumptions 
do not establish the commercial value either of fresh or 
stored manure, they are of some use in comparisons and gen- 
eralizations. The average manure, as it goes on the land, car- 
ries about 12 pounds of ammonia, 5 pounds of phosphoric 
acid, and 10 pounds of potash. Using the prices above, such 
manure is worth commercially about $3.00 a ton. 

The commercial evaluation must be applied with care be- 
cause of the many factors tending to vary the composition of 



P^ARM MANURE 



513 



the excrement. Litter, particularly, will exert a great influ- 
ence in this direction. Moreover, this mode of evaluation 
must never be confused with the much more important figure 
known as the agricultural value of a manure. The former 
is based on composition and assumed values of doubtful char- 
acter. The latter arises from the effect of the manure on crop 
yield. Obviously, a rational utilization of farm manure, as 
with any fertilizer, should strive for the highest return to 
an increment applied. A very good comparison between 
commercial and agricultural values may be cited from the 
Ohio experiments ^ with manure. The manure was treated in 
various ways and applied to maize in a three-year rotation 
of maize, wheat, and hay. Twenty-six crops were grown. 
The commercial evaluation is taken as 100 in every case. 



Table CX 
commercial and agricultur.\l evaluation of farm manure. 



Manure 


Commercial 
Value 


Agricultural 
Value 


Yard manure, untreated 


100 
100 
100 
100 
100 


152 


Yard manure, plus floats 


162 


Yard manure, plus acid phosphate . . 

Yard manure, plus kainit 

Yard manure, plus gypsum 


222 
192 
186 



291. Amount of manure produced by farm animals. — A 
well-fed moderately worked horse will produce daily from 
45 to 55 pounds of manure, of which 10 to 12 pounds is 
urine. A dairy cow, having a greater food capacity, will ex- 
crete from 70 to 90 pounds during the same period, of which 
20 to 30 pounds is liquid. Farm animals, especially sheep 
and swine, vary so much in size that a thousand pound 

^ Thome, C. E,, and others, The Maintenance of Fertility; Ohio Agr. 
Exp. Sta., Bui. 183, pp. 206-209, 1907. 



514 NATURE AND PROPERTIES OF SOILS 

weight of animal is the only fair and logical basis of calcu- 
lation. 

Table CXI 

MANURE EXCRETED BY VARIOUS FARM ANIMALS TO THE 1000 
POUNDS LIVE WEIGHT. 



Animal 


Pounds 
A Day 


Tons a 
Year 


Horse ^ 


50 
70 
40 
85 
34 
23 


9.1 


Cow 2 


12.7 


Steer ^ 


7.3 


Swine * 


15.5 


Sheep ^ 


6.2 


Poultry ^ 


4.2 







It is to be noted that these figures do not include litter, 
which, in cases of horses and cattle, will range from 15 to 20 
per cent, of the weight of the pure excrement. A working 
horse would be expected to produce from 10 to 11 tons of 
average manure a year, while a dairy cow on the same basis 
would produce 14 or 15 tons. 

Rough calculations as to manurial production from horses 
and cattle may be made from the food consumed by these 
animals.'^ It is assumed that 50 per cent, of the dry matter of 
the food appears in the excrement and that the necessary 
bedding equals one-half of the dry matter of the excrement. 

^Eoberts, I. P., and Wing, H. H., On the Deterioration of Farmyard 
Manure by Leaching and Fermentation ; Cornell Agr. Exp. Sta., Bui. 13, 
1889. Also, Eoberts, I. P., The Production and Care of Farm Manure; 
Cornell Agr, Exp. Sta., Biil. 27, 1891. Also, Watson, G. C, The Produc- 
tion of Manure; Cornell Agr. Exp. Sta., Bui. 56, 1893. 

^Thorne, C. E., Farm Manures, p. 97; New York, 1914. 

=• Thome, C. E., and others, The Maintenance of Fertility; Ohio Agr. 
Exp. Sta., Bui. 183, 1907. 

* Watson, G. C, The Production of Manure; Cornell Agr. Exp. Sta., 
Bui. 56, 1893. 

*Van Slyke, L. L., Fertilisers and Crops, p. 294; New York, 1912. 

* Hart, E. B., and Tottingham, W. E., General Agricultural Chemistry, 
p. 125; Madison, Wis., 1913, 



FARM MANURE 515 

Average manure (bedding plus excrement) is about 75 per 
cent, water. This means that from 100 pounds of mixed food 
there results 50 pounds of manurial dry matter, 25 pounds 
of litter, and 225 pounds of water or 300 pounds in all. The 
weight of the food consumed multiplied by three should give 
in a rough way the weight of the fresh excrement plus its 
litter. 

292. Loss of crop constituents in the production and 
handling of manure. — Any system of agriculture, whether it 
be grain farming, animal husbandry, or some specialized type 
such as trucking, must ultimately arrange for the addition 
of certain nutrients to replace those lost in the crop, in drain- 
age and through biological activity. It is evident, however, 
that even if all of the crop constituents were returned to the 
soil, a constant degi'ee of fertility would not be maintained, 
although the organic matter and possibly the nitrogen, if 
legumes were included in the rotation, might not greatly de- 
crease. The large loss of certain nutrients in the drainage 
water must always be considered in any rational system of 
soil fertility. 

Since farm manure lessens or even eliminates the need of a 
green-manure and at the same time offers a means of lower- 
ing the fertilizer bill, it is worth while to inquire what pro- 
portion of the nutrients contained in the crop may be re- 
turned to the soil in the resulting manure. The losses en- 
tailed are three: (1) those that occur in the handling and 
feeding of the crop, (2) those incurred as the food passes 
through the animal, and (3) those due to the handling and 
storage of the manure produced. 

293. Losses during manurial production. — A certain 
amount of every crop is lost before it is finally consumed by 
the animal. Such loss, while important, is usually small on 
every farm, especially when compared to the nutrients re- 
tained by the animal. Attention is, therefore, particularly 
directed towards those losses sustained by the food as it un- 



516 



NATURE AND PROPERTIES OF SOILS 



dergoes normal digestion. Some of the data available in this 
respect are quoted below: 

Table CXII 

percentage of original food constituents recovered 
in fresh manure. 



Animal 

Steers, Ohio ^ 

Steers, Penn.^ 

Steers, England ^ 

Milking cows, Illinois'*. 
Milking cows, Penn. ^ . . 
Milking cows, England ^ 
Heifers, England " . . . . 
Sheep, Ohio '* 



NH3 


P.O, 


61.0 


86.8 


69.4 


75.1 


95.5 


93.0 


80.3 


73.3 


84.6 


70.7 


71.8 


75.0 


77.8 


78.4 


68.0 


87.0 



K,0 



82.4 
81.2 
98.5 
76.0 
91.0 
90.0 
86.4 
91.5 



As might be expected, the data are quite variable, depend- 
ing on the age, condition, individuality and class of animal, 
and the character of the food. As a generalization and for 
purposes of calculation, it may be considered that three- 
fourths of the ammonia, four-fifths of the phosphorus, nine- 
tenths of the potash, and one-half of the organic matter are 
recovered in the manure.^ This means losses of about 25, 20, 

^ Thorne, C. E., Maintenance of Fertility; Ohio Agr. Exp. Sta., Bui. 
183, p. 200, 1907. 

^Frear, W., Losses of Manure; Pa. Agr. Exp, Sta., Bui. 63; Apr, 
1903. 

^Hall, A, D., Fertilisers and Manures, p. 180; New York, 1921. 

* Hopkins, C. G., Soil Fertility and Permanent Agriculture, p, 201, 
Boston, 1910. 

^Sweetser, W. S., The Manurial Value of the Excreta of Milch Cows; 
Pa. State Coll., Ann. Rep., 1899-1900, j>p. 321-351. 

"Hall, A. D., Fertilisers and Manures, p. 180; New York, 1921. 

^Wood, T. B., Losses in Making and Storing Farm Yard Manure; 
Jour. Agr. Sci., Vol. II, pp. 207-215, 1907-08. 

* Thome, C. E., Maintenance of Fertility; Ohio Agr, Exp, Sta., Bui. 
183, p. 202, 1907. 

"See Hopkins, C. G., Soil Fertility and Permanent Agriculture, p. 206; 
Boston, 1910. 

Also, Fippin, E. O., Live Stock and the Maintenance of Organic 



FARM MANURE 517 

10 and 50 per cent., respectively, for these constituents. While 
such losses are necessary and are usually compensated by the 
animal products, their magnitude must be considered in esti- 
mating the value of manure in the ordinary rotation. 

294. Losses due to handling and storage. — As about one- 
half of the ammonia and three-fifths of the potash of average 
farm manure are in a soluble condition, the possibility of loss 
by leaching is usually great, even though the manure is not 
exposed to especially heavy rainfall. The loss of phosphorus 
is also of some consequence. In addition, decomposition, espe- 
cially that of an aerobic nature, will cause a rapid waste of 
ammonia, one-half of that present being especially susceptible. 
Packing and moistening the manure will change the decay 
from aerobic to anaerobic, thus reducing the waste of am- 
monia while encouraging the simplification of the manurial 
constituents. Tight floors in the stables and impervious bot- 
toms in the manure pit or under the manure pile will con- 
siderably diminish leaching losses. 

It is impossible, in quoting figures for waste of manure, 
to separate the losses due to fermentation and putrefaction 
from those due to leaching. The two processes go on simul- 
taneously, the loss from one source being dependent, to a cer- 
tain extent, on the other. It is only the nitrogen, however, 
that may be lost hy both decomposition and leaching, the min- 
erals being wasted only through the latter avenue. 

While the figures are variable (Table CXIII), it is easilj^ 
seen that one-half of the ammonia and potash and one-third of 
the phosphoric acid are readily lost under fairly careful meth- 
ods of storage. On the average farm where manure very often 
remains outside for several months, the losses will run much 
higher, easily amounting to 50 per cent, of the organic mat- 
ter, 60 per cent, of the ammonia, 40 per cent, of the phos- 

Matter in the Soil; Jour. Amer. Soc. Agron., Vol. 9, No. 3, pp. 97-105, 
Mar. 1917. 

Also Armsby, H. P., and Fries, J. A., Net Energy Values of Feeding 
Stuffs for Cattle; Jour. Agr. Res., Vol. Ill, pp. 435-491, 1915. 



518 NATURE AND PROPERTIES OF SOILS 

phoric acid, and 65 per cent, of the potash. This means a loss 
of at least one-half of the nutrient constituents of the ma- 
nure and considerably over one-half of the fertilizing value, 
since the elements wasted are those most readily available to 
plants. Considering the losses which the food sustains during 
digestion and the waste of the manure in handling and stor- 
age, it cannot be expected that more than 25 per cent, of the 

Table CXIII 

losses from manure through leaching and 
fermentation. 



Kind of Manure 


Horse ^ 
183 


Horse ^ 


Horse '^ 


Cow^ 


Cow' 


Steer ■* 


Days exposed. . . . 


183 


274 


183 


77 


91 


Percentage loss of 














ammonia 


36 


60 


40 


41 


31 


30 


Percentage loss of 














phosphoric acid 


50 


47 


16 


19 


19 


23 


Percentage loss of 














potash 


60 


76 


34 


8 


43 


58 



organic matter, 30 per cent, of the ammonia, 50 per cent, of 
the phosphoric acid, and 30 per cent, of the potash of the 
original crop will reach the land.^ Even if leaching losses 

^ Roberts, I. P., and Wing, H. H., On the Deterioration of Farmyard 
Manure by Leaching and Fermentation; Cornell Agr. Exp. Sta., Bui. 13, 
1889. 

^Schutt, M. A., Barnyard Manure. Canadian Dept. Agr., Centr. Exp. 
Farms, Bui. 31, 1898. 

^ Thome, C. E., Farm Manures, p. 146; New York, 1914. 

* Thorne, C. E., and others, The Maintenance of Fertility ; Ohio Agr. 
Exp. Sta., Bui. 183, 1907. 

^ Voelcker and Hall have drawn up recommendations for the compen- 
sation of the out-going English tenant for manure produced on the farm 
but not realized on. They suggest that he receive pay at fertilizer prices 
for one-half of the nitrogen, three-fourths of the phosphoric acid, and 
all of the potash contained in the food consumed during the last year 
of tenancy. For the second, third, and fourth years previous, the com- 
pensation value shall be one-half that of the year immediately preced- 
ing. Voelcker, A., and Hall, A. D., The Valuation of Unexhausted 
Manures; Jour. Eoy. Agr. Soc. Eng., Vol. 63, pp. 76-114, 1902. 



FARM MANURE 



519 



OR.G/R/\/JC 



^O^ K^O 



^£-r/^//V£D BY^N/MAL 



Lost //v h/^/^dl /ng 



/^dd£:d to TH£30/L. 




Fig. 62. — Diagram showing the proportion of the important constituents 
of the food retained by the animal, lost in the handling and the 
storage of the manure and applied to the soil under ordinary 
conditions. 



were not important, a self-sustaining system of agriculture 
could not be established by the use of farm manure alone, as 
organic matter is the only constituent that would be added 
to the soil in amounts that approach the magnitude of the 

loss.' 

* Fippin, E. O., Live Stock and the Maintenance of Organic Mat- 
ter in the Soil; Jour. Amer. Soc. Agron., Vol. 9, No. 3, pp. 97-105, 
Mar. 1917. 



520 NATURE AND PROPERTIES OF SOILS 

295. Two phases of manurial practice. — A commercial 
fertilizer, if made properly, may be kept for long periods 
unimpaired and is always in a condition for instant applica- 
tion to the soil. The only problem confronting the farmer is 
the profitable application of such material. Storage is a 
minor factor. Farm manure, on the other hand, although a 
true fertilizer, presents, because of its peculiar characteris- 
tics, serious complications. As it is subject to tremendous 
losses by leaching, putrefaction, and fermentation, its han- 
dling and storage, if the latter becomes necessary, is as im- 
portant as its rational utilization on the land. Manurial prac- 
tice, therefore, is logically discussed under two headings: 
(1) handling and storage, and (2) utilization of the manure 
in the field. 

296. Care of manure in the stalls. — Considerable loss to 
manure occurs in the stable, due to decomposition and leach- 
ing. Before the urine can be absorbed by the litter, it is 
likely to decay and leach away in considerable amounts. 
Therefore, the first care is to the bedding, which should be 
chosen for its absorptive properties, its cost, and its cleanli- 
ness. The following table ^ shows the approximate absorptive 
capacity of some common litters. (Table CXIV, page 521.) 

The amount of litter to be used is determined by the char- 
acter of the food. If the food is watery, the bedding should 
be increased. In general, the litter amounts to about one- 
fourth of the dry matter of the food consumed. Sheep re- 
quire about a pound of bedding a head, cattle from eight to 
ten pounds, and horses from ten to fifteen pounds. No more 
litter than is necessary to keep the animal clean and to ab- 
sorb the liquid manure should be used, as the excrement is 

*Beal, W. H., Barnyard Manure; U. S. Dept. Agr., Farmers' Bui. 
192, 1904. 

W^hisenand, J. W., Water-iiolding Capacities of Bedding Materials 
for Live Stock, Amounts Required to Bed AninMls, and Amounts of 
Manure Saved by Their Use; Jour. Agr. Ees., Vol. XIV, No. 4, pp. 
187-190, July 19i8. 



FARM MANURE 521 

Table CXIV 
absorptive power op bedding for water. 



Material 



Percentage of 
Water Eetained 



Mixed shavings. . . . 
Mixed sawdust. . . . 
Fine pine shavings. 

Muck 

Wheat straw 

Oats straw 

Peat 

Peat moss 



124 
160 
185 
200 
210 
250 
600 
1300 



thus diluted unnecessarily with material which often does 
not carry large quantities of available fertilizing ingredients. 

The next care is that floors should be tight, so that the 
free liquid cannot drain away but will be held in contact with 
the absorbing materials. The preserving of manures in stalls 
with tight floors has been for years a common method of han- 
dling dung in England. The trampling of the animals, and 
the continued addition of litter as the manure accumulates, 
explain the reason for the success of the method. The follow- 
ing data, from Ohio,^ show the relative recovery of food ele- 
ments in manure produced on a cement floor and on an earth 
floor, respectively. The experiment was conducted with steers 
over a period of six months. Even with a good dirt floor, the 
leaching losses are considerable. (Table CXV, page 522.) 

297. Hauling directly to the field.=^ — Where it is possible 

^ Thome, C. E., Maintenance of Fertility; Ohio Agr. Exp. Sta., Bui, 
183, p. 199, 1907. 

* Good discussions of handling farm manure are as follows : 

Hart, E. B., Getting the Most Profit from Farm Manure; Wis. Agr. 
Exp. Sta., Bui. 221, 1912. 

Beal, W. H., Barnyard Manure; U. S. Dept. Agr., Farmers' Bui. 192, 
1904. 

Roberts, I. P., The Fertility of the Land, Chapter IX, pp. 188-213; 
New York, 1904. 



522 



NATURE AND PROPERTIES OF SOILS 



Table CXV 

recovery of pood elements in manure produced on cement 
floor; on earth floor. 



Constituents 


Percentage Eecovery 




Cement Floor 


Earth Floor 


Ammonia 


74.7 
77.5 

87.8 


62.4 


Phosphoric acid 


78.9 


Potash 


78.4 


Average 


80.0 


73.2 







to haul directly to the field, this practice is to be advised, 
since opportunities for excessive losses by leaching and fer- 
mentation are thereby prevented. Manure may even be 
spread on frozen ground or on the top of snow, provided the 
land is fairly level and the snow is not too deep. This sys- 
tem saves time and labor, and when leaching does occur the 
soluble portions of the manure are carried directly into the 
soil. The practice of allowing the manure so spread to lie 
on the surface of the land all winter is sometimes questioned, 
especially in New England.^ On sandy soils it may some- 
times be better practice to store the manure until spring. 

298. Piles outside. — Very often it is necessary to store 
manure outside, fully exposed to the weather. When this is 
the case, certain precautions must be observed. In the first 
place, the pile should be located on level ground far enough 
from any building that it receives no extra water in times 
of storm. The sides of the heap should be steep enough to 
shed water readily, while the depth of the pile should be such 
as to allow little leaching even after heavy storms. The earth 
under the manure may be slightly dished in order to prevent 

'■ Brooks, W. P., Methods of Applying Mamire; Mass. Agr. Exp. Sta., 
Bui. 196, Sept. 1920. 



FARM MANURE 523 

loss of excess water. If possible, the soil of tlie depression 
should be puddled, or, better, lined with cement. 

The manure should be kept moist in diy weather in order 
to decrease aerobic action. Each addition of manure should 
be packed in place, the fresh on and above the older. This 
allows the gases from the well-rotted dung to pervade the 
fresher and looser portions, thus quickly establishing the 
anaerobic conditions so essential to economic and favorable 
fermentation. 

Placing fresh manure in small heaps in the field to be 
spread later, is, in the first place, poor economy of labor. 
Moreover, it encourages loss by decay, while at the same time 
the soluble portions of the pile escape into the soil imme- 
diately underneath. There is thus a poor distribution of the 
essential elements of the dung, and when the manure is finally 
spread, an over-feeding of plants at one point and an under- 
feeding at another results. A low efficiency of the manure 
is thus realized. This method of handling manure is not to 
be recommended, 

299. Manure pits. — Some farmers, especially if the 
amount of manure produced is large, find it profitable to con- 
struct manure pits of concrete. These pits are usually rec- 
tangular in shape with a shed covering. Often one or even 
both ends are open to facilitate the removal of the manure. 
In such a structure, leaching is prevented by the solid bottom 
while the roof allows a better control of moisture conditions. 
By keeping the manure carefully spread and well moistened, 
putrefaction may proceed with a minimum loss of nitrogen. 
Some European dairymen even go so far as to utilize a cis- 
tern, into which is shoveled both the liquid and the solid 
manure. Later when decomposition has proceeded suffi- 
ciently, the material is pumped out and applied to the land. 
This method is not to be advocated in this country except 
under special conditions, owing to the cost of handling. 

300. Covered yards. — Another method of storage is by 



524 NATURE AND PROPERTIES OF SOILS 

means of a covered barnyard. Such a yard should have a 
more or less impervious floor. The manure is spread out in 
the yard and is kept thoroughly packed as well as damp by 
the animals. This is a common method of handling the ma- 
nure in the fattening of steers in the Middle West and pro- 
duces manure at a minimum loss, providing hogs are not al- 
lowed to follow the steers. The storage of manure in deep 
stalls, a favorite method in England, is similar to this system 
and has been shown to be very economical. It also affords an 
opportunity for the mixing of the manure from different 
classes of animals. The desirability of this has already been 
shown in the case of horse and cow excrements. The advan- 
tages of trampling, so far as the keeping qualities of manure 
are concerned, are clearly shown by the following figures 
taken from the work of Frear : ^ 

Table CXVI 
loss of manure in covered sheds. 



Condition 


Percentage Loss op 




NH3 


K3O 


P.0« 


Covered and tramped 


5.7 
34.1 


5.5 

19.8 


8.5 


Covered and untramped 


14.2 







Throwing manure in heaps under a shed and allowing hogs 
to work the mass over, is a desirable practice so far as food 
utilization is concerned. It interferes, however, with a proper 
and economical packing of the manure. The question to be 
decided is whether the added food value of the manure over- 
balances the extra losses by decomposition incurred by the 
rooting of the swine. 

301. Increased value of protected manure. — From the 
previous discussion, it is evident that a well-protected and 

"■ Frear, W., Losses of Manure; Pa. Agr. Exp. Sta., Bui. 63, 1903. 



FARM MANURE 



525 



carefully preserved manure will be higher in available plant 
constituents than one not so handled. Moreover, the agricul- 
tural value of such manure will be higher. This is shown 
by actual tests from Ohio.^ Over a period of fourteen years, 
in a three-years' rotation of maize, wheat, and hay, a stall 
manure gave a yield 38 per cent, higher than that with a yard 
manure. 

Table CXVII 
increase yields from yard and stall manure. 



Manure 


Average Annual Increase to 
THE Acre 




Maize 
14 Crops 


Wheat 
14 Crops 


Clover 
11 Crops 


Yard, 8 tons to the rota- 
tion 


18.6 bus. 
23.6 bus. 

26.8% 


9.5 bus. 
10.9 bus. 

14.7% 


801 lbs 


Stall, 8 tons to the rota- 
tion 


1395 lbs 


Increase, stall over yard 
manure 


74.1% 





In New Jersey, fresh manure showed a gain in crop yield 
53 per cent, higher than leached manure over the three years 
immediately following the application. Such figures are 
worthy of careful consideration. 

302. Application of manure.— In the application of ma- 
nure to the land, the same general principles observed in the 
use of any fertilizer should be kept in mind. Of these, fine- 
ness of division and evenness of distribution are of prime im- 
portance. The efficiency of the manure may be raised con- 
siderably thereby. Moreover, it is generally better, since the 

^Thorne, C. E., and others, PIa7is and Summary Tables of tJie Experi- 
ments at the Central Farm; Oliio Agr. Exp. Sta., Cire. 120, p. 112, 
1912. 



526 



NATURE AND PROPERTIES OF SOILS 



supply of manure is usually limited in diversified farming, to 
decrease the amounts at each spreading and cover a greater 
acreage. Thus, instead of adding 20 tons to the acre, 10 tons 
may be applied and twice the area covered. Applications 
could then be made oftener and a larger and quicker net 
return realized for each ton of manure. With manure, as 
with any fertilizer, the yield to the acre is not so important 
as the crop increase for a given increment of manure added. 
The influence of rate of application on increased yield to a 
ton of manure is shown bj' the Ohio ^ experiments over eight- 
een years in a three-year rotation of wheat, clover and pota- 
toes, the manure being placed on the wheat. 



Table CXVIII 

increased yield to the ton when manure is applied in 
different amounts. ohio experiment station. 



Eate 


Wheat 

(bus.) 


Clover 
(lbs.) 


Potatoes 

(bus.) 


4 tons to the acre 

8 tons to the acre 

16 tons to the acre 


1.34 
.94 
.70 


177 

150 

99 


3.81 
2.79 
2.76 



Not only is the increased efficiency from the smaller appli- 
cation apparent, but a greater recovery of the manurial fer- 
tility in the crops also results. The Ohio experiments show 
that in the first rotation after the manure is applied, a 25 to 
30 per cent, higher recovery may be expected from the 8 tons 
treatment than from the 16 tons. 

Evenness of application and fineness of division are greatly 
facilitated by the use of a manure-spreader. This also makes 
possible the uniform application of small amounts of manure, 

^ Thorne, C. E., and others^ Plans and Summary Tables of the Experi- 
ments at tJie Central Farm; Ohio Agr. Exp. Sta., Circ. 120, p. 108, 
1912. 



FARM MANURE 527 

even as low as 5 or 6 tons to the acre. It is impossible to 
spread so small an amount by hand and obtain an even dis- 
tribution. Moreover, a spreader lessens the labor and more 
than doubles the amount of manure one man can apply a day. 
When any considerable quantity of manure is to be handled, 
a manure-spreader will pay for itself in a season or two at the 
most. 

Whether manure should be plowed under or not depends 
largely on the crop on Avhich it is used. On timothy it is 
spread as a top dressing. Ordinarily, however, it is plowed 
under. This is particularly necessary if the manure is long, 
coarse, and not well-rotted. It should not be turned under 
so deep, however, as to prevent ready decay. If manure is 
fine and well decomposed, it may be harrowed into the surface 
soil. The method employed depends on the crop, the soil, and 
the condition of the manure. The amount to be applied va- 
ries considerably. Eight tons to the acre would be a light 
dressing, 15 tons a medium dressing, and 25 tons heavy for 
an ordinary soil. In trucking land, however, as high as 50 
or 100 tons are often used. 

303. Reinforcement of manure. — The reinforcement of 
farm manure is designed to accomplish two things in the han- 
dling of this product: (1) cheeking loss due to leaching and 
decomposition, and (2) balancing the manure and rendering 
its agricultural value higher. Four chemicals may be used 
in this reinforcement: gypsum (CaSO^), kainit (mostly 
KoSOJ, acid phosphate (CaH.CPOJ, -f CaSOJ, and floats 
(raw rock phosphate, Ca3(P04)2). 

Gypsum and kainit are supposed to react with the ammonia 
of the manure, changing it to ammonium sulfate, a stable 
compound. As gypsum is rather insoluble, its action is prob- 
ably slow. It may be applied either in the stable or on the 
manure pile, usually at the rate of 100 pounds to the ton. 
It has no balancing effect. Kainit is soluble and because of 
its caustic tendencies should not come into contact with the 



528 NATURE AND PROPERTIES OF SOILS 

feet of the animals. It must not be spread on the manure 
until the stock are out of the way. Since manure is unbal- 
anced as to phosphorus, the agricultural value of kainit is 
slight. When applied, it is generally used at the rate of 50 
pounds to the ton of manure. 

Acid phosphate is partially soluble and will not only react 
readily with the ammonia but will tend to raise the phos- 
phorus content to the proper point. From 40 to 80 pounds 
of acid phosphate are generally recommended to a ton of 
average farm manure. It should not be allowed to come into 
contact with the feet of farm animals. 

Raw rock phosphate, or floats, is a very insoluble compound, 
and consequently reacts but slowly with the soluble constitu- 
ents of manure. Carrying such a large percentage of phos- 
phorus, it tends to balance the manure and to raise its agri- 
cultural value. It is supposed that the intimate relationship 
between the phosphate and the decaying manure increases the 
availability of the former to plants when the mixture is added 
to the soil. The reinforcement is usually at the rate of 75 
to 100 pounds to a ton of manure. 

Experimental data have shown that these various rein- 
forcements have no particular effect on the nature, function, 
and number of the bacterial flora. Their conserving influ- 
ence, if any, when the manure is exposed, might be in check- 
ing leaching and in preventing loss of ammonia. The follow- 
ing figures from Ohio experiments ^ show how slight this con- 
serving effect is. The reinforcement was at the rate of 40 
pounds to the ton. (See Table CXIX, page 529.) 

It is immediately evident that kainit and gypsum do not 
conserve the manure, and, although acid phosphate and floats 
show some influence, it is slight and evidently well within the 
experimental error. The principal benefit from reinforcing 
manure, if any, must, therefore, be as a balancing agent. The 

* Thorne, C. E., and others, The Maintenance of Fertility; Ohio Agr. 
Exp. Sta., Bui. 183, p. 206, 1907. 



FARM MANURE 



529 



Table CXIX 

conserving effect of reinforcing agents on manure 
exposed for three months. 



Treatments 


Ratio Values of a 
Ton of Manure 


Percentage 
Loss 




IN JANUARY 


IN APRIL 




No reinforcement 


100 

93 

102 

128 
106 


64 
67 
66 
93 
75 


36 


With gypsum 


38 


With kainit 


35 


With floats 


27 


With acid phosphate 


29 



figures from Ohio ^ over a period of fourteen years in a rota- 
tion of maize, wheat, and hay may be taken as evidence re- 
garding this point. The manure treated and handled as above 
was added to the maize at the rate of 8 tons to the acre. 

It is evident that the principal benefit of reinforcing ma- 
nure lies in the balancing influence and that acid phosphate 
and floats are the most desirable agents. It is also evident 

Table CXX 

influence of reinforcing on the effectiveness 
of manure. 





A.VERAGE Annual Increase to the Acre 


Ratio Value 








OF Increase 


Treatment 












Corn 


Wheat 


Hay 


Per Ton of 




1.4 Crops 


14 Crops 


11 Crops 


Manure 


No reinforcement. . 


18.6 bus. 


9.5 bus. 


801 lbs. 


100 


With g^-^^sum ...... 


23.6 bus. 


11.6 bus. 


916 lbs. 


119 


With kainit 


2.3.7 bus. 


11.3 bus. 


1156 lbs. 


115 


With floats 


25.0 bus. 


12.9 bus. 


1578 lbs. 


138 


With acid phosphate 


30.6 bus. 


15.1 bus. 


1853 lbs. 


161 



^ Thorne, C. E., and others, Plans and Summary Tables of the Experi- 
ments at the Central Farm; Ohio Agr. Exp. Sta., Circ. 120, p. 112, 
1912. 



530 NATURE AND PROPERTIES OF SOILS 

that floats, if added in money values equal to acid phosphate, 
should be about as satisfactory as a reinforcing material. 

304. Lime and manure. — Very often it would be a sav- 
ing of labor to apply lime and manure to the soil at the same 
time. This can readily be done with the carbonated forms. 
Such lime may be mixed with the manure, either in the stable 
or in the pile, without any danger of detrimental results. The 
close union of the lime and manure may increase the effective- 
ness of the former and at the same time promote a better type 
of decomposition in the latter. If the soil is really in need of 
calcium, however, a separate application of lime is much bet- 
ter, as the amount of calcium added with the manure is never 
large. Caustic compounds of lime such as calcium oxide 
(CaO) and calcium hydroxide (Ca(0H)2) must be kept from 
manure. These forms readily react with the ammonium car- 
bonate coming from the urea, and cause the Tberation of 
ammonia, which may be readily lost to the air: 

CON,H, + 2H2O = (NHJXOg 
(NHJ2CO3 + Ca(0H)2 = CaCOs + 2NH,0H 

A stable or shed containing manure may be at once deodor- 
ized by the use of quicklime, but with the loss of much nitro- 
gen. If the manure is to be worked into the surface soil, the 
caustic lime may be applied some days before and if it is in 
thorough contact with the soil, it will change to the carbonate 
before the manure is added. When the manure is plowed 
under, the lime is best added after the plowing and thor- 
oughly harrowed in as the seed-bed is prepared. 

305. Manure and composting. — A compost is usually 
made up of alternate layers of manure and some vegetable 
matter that is to be decayed. Layers of sod or of soil high in 
organic matter are often introduced. The manure supplies 
the decay organisms and starts biological activities. The 
foundation of such a compost is usually soil, and the pile is 
preferably capped with earth. The mass should be kept 



FARM MANURE 



531 



moist in order to prevent loss of ammonia and to encourage 
vigorous bacterial action. Acid phosphate or raw rock phos- 
phate and a potash fertilizer are often added, to balance up 
the mixture and make it a more effective fertilizer. Lime is 
also introduced, to react with such organic acids as may tend 
to interfere with proper decay. Undecayed plant tissue, 
such as sod, leaves, weeds, grass, sticks, or organic refuse of 
any kind, may thus be changed slowly to a form which will be 
valuable in building up the soil and in nourishing plants. 
Even garbage may be disposed of in such a manner. 

306. Residual effects of manure. — No other fertilizer 
exerts such a marked residual effect as does farm manure. 
As it is applied in large amounts, its physical and biological 
influences are of necessity very great and persist for a con- 
siderable time. As only about one-half the nutrients of farm 
manure are readily available, the residual effect of its fertiliz- 
ing elements carry over into succeeding years. Hall ^ pre- 
sents the following comparative data regarding the recovery 
of nitrogen from various fertilizers. The crop used was man- 
golds. The low reco^'ery of the nitrogen from the manure is 
of especial note. There is no reason to believe that the pot- 
ash of the manure would be any more readily available and 
the phosphoric acid would certainly show a lower recovery. 

Table CXXI 
recovery of nitrogen in a crop of mangolds. 



Sodium nitrate. . 
Ammonium salts. 

Rape cake 

Farm manure. . . 



Rate to 
THE Acre 



550 lbs. 

400 lbs. 

2000 lbs. 

14 tons 



Yield in 
Tons 



17.95 
15.12 
20.95 
17.44 



Percentage 

Eecovery of 

Nitrogen 



78.1 
57.3 
70.9 
31.6 



^Hall, A. D., Fertilisers and Manures, p. 210; New York, 1921. 



532 NATURE AND PROPERTIES OF SOILS 

The length of time through which the effects of an appli- 
cation of farm manure may be detected in crop growth is 
very great. Hall ^ cites data from the Rothamsted Experi- 
ments in which the effects of eight yearly applications of 14 
tons each were apparent forty years after the last treatment. 
This is an extreme case. Ordinarily, profitable increases may 
be obtained from manure only from two to five years after 
the treatment.- The fact remains, nevertheless, that of all 
fertilizers, farm manure is the most lasting and lends the most 
stability to the soil. 

307. The place of manure in the rotation.'' — With 
trucking, garden, and greenhouse crops, the applications of 
large amounts of manure year after year have proven advis- 
able. As a matter of fact, manure has shown itself, especially 
if balanced with phosphoric acid, to be the best fertilizer for 
intensive operations. This is due not only to the nutrients 
carried by the manure, but to the large amounts of easily 
decomposed organic matter that are at the same time intro- 
duced. In a rotation involving the staple crops, such as maize, 
oats, wheat, hay, and the like, less intensive applications are 
advisable, not only because of a lack of manure but because 
the return to a ton of manure applied must be raised as high 
as possible. On the average farm, there is less than one ton 
of manure produced to an acre of arable land. Moreover, the 
return from manure will vary according to its place in the 
rotation. This has proved to be the case with commercial 
fertilizers and the fact is becoming more and more apparent 
with farm manure. 

In general, meadows and pastures derive more benefit from 
manure, either residually or directly, than any other crop. 

^ Hall, A. D., Fertilisers and Manures, p. 213; New York, 1921. 

='Voelcker, A., and Hall, A. D., The Valuation of Unexhausted 
Manure Obtained by the Consumption of Foods hy Steele; London, 
1903. 

"See Thorne, C. E., Farm Manures, Chaps. XI and XIII, New York, 
1914. 



FARM MANURE 



533 



The long tests conducted by the Pennsylvania and Ohio ex- 
periment stations ^ have established this fact. The following 
data from Illinois - may be cited, comparing the response of 
maize and oats when manured to the increased yield of clover 
receiving the same treatment. (See Table CXXII, page 534.) 



CROP 



K2O - 




FOOD LOSSES 



- 50% 

NHj- 25 " 

26 •• 



10 



MANURIAL LOSSES 



OM 


-50% 


NHs 


-60 )- 


P^Os 


-40 » 


KzO 


-65" 



.(^W 



'^^^^^^^^^^^^^'^^^mm^^m^Mm^^?;^^^ 



PERCENTAGE OF THE CONS- 
TITUENTS OF CROP 
ADDED TO SOIL 



OM - 25% 



N 

LEACHING 

Fig. 63. — Diagram showing the proportion of the harvested crop added to 
the soil in farm manure under average conditions. 



It is easy to see that a liberal dressing of manure on the 
hay and pasture will markedly increase the crop. Neverthe- 
less, as manure is available in limited amounts on the average 
farm and as commercial fertilizers will give almost as good 
returns on hay, it is generally considered judicious, except in 

* Hunt, T. F., General Fertilizer Experiments ; Ann. Eep. Penn. Agr. 
Exp. Sta., 1907-1908, pp. 68-93. 

Thome, C. E., and others, Plaiis and Summary Tables of the Experi- 
ments at the Central Farm; Ohio Agr. Exp. Sta., Circ. 120, np. 101- 
105, 1912. 

" Hopkins, C. G., Thirty Years of Crop Rotation in Illinois; 111. Agr, 
Exp. Sta., Bui. 125, p. 337, 1908. 



534 



NATURE AND PROPERTIES OF SOILS 



Table CXXII 
influence of manure on maize, oats, and clover. 



Treatment 


Average Percentage 
Increase 


Eatio Value of 
Increase 




Maize and 
Oats 


Clover 


Maize and 
Oats 


Clover 


Manure alone. . 
Manure, lime 
and phosphate 


11 
30 


92 
141 


100 
162 


134 

206 



certain cases, to reserve most of the manure for other crops. 
The top dressing of meadows is, however, always an allowable 
practice, especially on new seeding or on hay land that is 
soon to be plowed for maize. 

As a food producer, maize has no close rival. Where the 
climate is favorable, a 75-bushel crop of maize is as easily 
secured as 40 bushels of wheat or 300 bushels of potatoes to 
the acre. Moreover, the maize stover may be made more valu- 
able as roughage than the straw of oats, wheat, or rye. The 
maize plant must have, however, for its successful growth 
plenty of available nitrogen. In addition, its response to 
abundant organic matter indicates the utilization of certain 
organic compounds. These considerations argue for the use 
of most of the farm manure on the maize when this crop is 
important, especially if the supply of manure is limited. 
Again the maize crop is ready for the manure in the spring 
and is generally grown on land where the excreta may be 
distributed during the previous winter and fall. 

Potatoes are a spring crop and where they are prominent 
in the rotation may receive liberal applications of manure. 
If potatoes are the money crop, this should by all means be 
the practice. Oats, because of the tendency to lodge, gener- 
ally follow maize or potatoes as a residual feeder, receiving, if 
necessary, a dressing of commercial fertilizer. If manure is 



FARM MANURE 535 

used on fall wheat, a great loss of manurial value is incurred, 
due to the necessity of storage during the summer months. 
Moreover, commercial fertilizers liig-li in phosphorus are so 
convenient and effective on wheat that the use of manure on 
this crop is becoming rather uncommon, although manure 
may be used to advantage as a fall and winter dressing, since 
it not only stimulates the wheat but is of great value to the 
new seeding as well. Where cotton and tobacco are the staple 
crops, they should receive at least a part of the manure pro- 
duced. The value of manure in orchards should not be over- 
looked, especially on sandy soils. The up-keep of organic 
matter, the conservation of moisture, and the nutrients sup- 
plied are as important here as in any phase of soil manage- 
ment. 

308. Resume. — Barnyard manure, from the standpoint 
of soil fertility, is the most valuable by-product of the farm. 
A careful farmer will, therefore, attempt to utilize it in the 
most economical way. The handling of manure in such a 
manner that only a minimum waste occurs from the time 
the manure is voided until it has reached the land is not an 
easy problem. Manure is so susceptible to the loss of valuable 
ingredients, both by leaching and by decay, that careful 
methods must be employed. Tight floors in the stable and 
covered sheds or manure pits are always advisable. Hauling 
immediately to the field is the wisest procedure, yet even with 
the best of care more than 50 per cent, of the fertilizing value 
is usually lost. The problem of rational manurial utilization 
is not solved, however, by careful handling and storage alone. 
Manure must be applied in such a condition, in such amounts 
and at such a point in the rotation as to realize a reasonable 
return for every increment applied. The reinforcement of 
farm manure with phosphoric acid is by no means an unim- 
portant feature. In fact, all of the principles which are ob- 
served in the profitable utilization of commercial fertilizers 
should be adhered to in the use of farm manures. 



536 NATURE AND PROPERTIES OF SOILS 

A permanent system of agriculture evidently cannot be 
established by merely returning all the manure possible to 
the land, as approximately only 25 per cent, of the organic 
matter, 30 per cent, of the ammonia, 50 per cent, of the phos- 
phoric acid, and 30 per cent, of the potash of the food con- 
sumed on the farm ever reach the land in the manure. Never- 
theless, it is certainly worth the while of a farmer to use 
some care in handling this product and some thought as to 
its rational utilization in the field. Even if the manure 
should aid only in the up-keep of organic matter, the effort 
would be worth while. Reasonable care in the handling of 
farm manure will save this country thousands of pounds of 
manurial fertility which are now utterly lost and at the same 
time increase by thousands of dollars the food production. 



CHAPTER XXV 
GREEN-MANURES ^ 

From time immemorial the turning-iinder of a green-erop 
to supply organic matter to the soil has been a common agri- 
cultural practice. Records show that the use of beans, vetches, 
and lupines for such a purpose was well understood by the 
Romans, who probably borrowed the practice from nations 
of greater originality. The art was lost to a great extent dur- 
ing the Middle Ages, but was revived again as the modern 
era was approached. At the present time, green-manuring 
is considered a part of a well-established system of soil man- 
agement, and is given a place, when possible, in every ra- 
tional plan for permanent soil improvement. 

309. Importance of green-manures. — The plowing under 
of some succulent rapid-growing crop, such as oats, rye, or 
clover, tends to bring about three desirable soil conditions; 
additional organic matter, a betterment of the physical con- 
dition of the soil, and a rise in the nitrogen content of the 
land, if the crop is an inoculated legume. If conditions are 

^ Penny, C. L., Clover Crops as Green Manures; Del. Agr. Exp. Sta., 
Bui. 60, 1903. 

Storer, F. H., Agriculture, pp. 137-175; New York, 1910. 

Lipman, J. G., Bacteria in Relation to Country Life, Chapter XXIV, 
pp. 237-263; New York, 1911. 

Piper, C. v., Leguminous Crops for Green Manuring ; U. S. Dept. Agr., 
Farmers' Bui. 278, 1907. 

Spillnian, W. J., Renovation of Worn-out Soils; U. S. Dept. Agr., 
Farmers ' Bui. 245, 1906. 

Pieters, A. J., Green Manuring: A Eevieic of the Americayi Experi- 
ment Statio)i Literature ; Jour. Amer. Soe. Agron., Vol. 9, No. 2, pp. 
62-82, Feb. 1917; Vol. 9, No. 3, pp. 109-126, Mar. 1917; Vol. 9, No. 4, 
pp. 162-190, Apr. 1917. 

537 



538 NATURE AND PROPERTIES OF SOILS 

favorable, an increase in crop production slionld result. 
Where there is a shortage of farm maiiurt", the practice be- 
comes of special importance since roots and crop residues are 
usually insufficient to maintain the organic content of the 
soil. Even where manure is available, a green-manuring 
crop now and then in the rotation does much towards sus- 
taining normal production. 

The effects of turning under green plants are both direct 
and indirect — direct as to the influence on the succeeding crop, 
and indirect as to the soil so treated. In the first place, cer- 
tain ingredients are actually added to the soil by such a 
procedure. The carbon, oxygen, and hydrogen of plants come 
largely from the air and water, and the plowing-under of a 
crop, therefore, increases the store of such constituents in the 
soil. The compounds that result from crop decay increase 
the absorptive power of the soil, and promote aeration, drain- 
age, and granulation — conditions that are extremely impor- 
tant in successful plant growth. If the crop turned under is 
a legume and the nodule organisms are active, the store of soil 
nitrogen is markedly augmented, a point of extreme impor- 
tance in fertilizer practice. 

Green-manures may function also as cover-crops, insofar as 
they take up the extremely soluble plant nutrients and pre- 
vent them from being lost in the drainage water. The nitrates 
of the soil are of particular importance in this regard as they 
are very soluble and are absorbed only slightly by the soil 
complexes. Besides this, green-manures, especially those with 
long roots, tend to carry nutrients upward from the subsoil 
and when the crop is turned under this material is deposited 
within the root zone. Again, the added organic material acts 
as a food for soil organisms, and tends to stimulate biological 
changes to a marked degree. This biological action is espe- 
cially important in the production of carbon dioxide, am- 
monia, nitrates, and organic compounds of various kinds, 
which are necessary in plant nutrition. 



GREEN-MANURES 539 

310. Gain of constituents by green-manuring'. — In an 
average crop of g:reon-mamire, from five to ten tons of mate- 
rial are turned under. Of this, from one to two tons are dry 
matter, and from four to eight tons water. Of this dry matter, 
a great proportion is carbon, hydrogen, and oxygen. It might 
seem at first thought that such an addition is pure gain as 
far as carbon and carbonaceous matter are concerned. Such 
is not the case. Large amounts of carbon are lost continu- 
ously in drainage, to say nothing of that removed by crops or 
that which is respired by the soil as carbon dioxide. It has 
already been shown, from results obtained with the Cornell 
lysimeters, that a heavy soil will yearly lose over 250 pounds 
of carbon, in drainage alone (see par. 220). This is approxi- 
mately equivalent to a 2-ton application of green-manure. 
Although the loss of carbonaceous material is considerable, 
even during the period that the green-manuring crop is being 
grown, nevertheless the practice offers a rapid as well as a 
natural means of increasing the soil organic matter. 

The mineral parts of the turned-under crop came from the 
soil originally and they are merely turned back to it again 
and represent no gain. As they return, however, they are in 
intimate union with organic materials, and are thus readily 
available as the decay processes go on. Indeed they are prob- 
ably more readily available than they previously were, when 
the green-manuring crop acquired them. 

The amount of nitrogen added to a soil if the green-manure 
is a legume ^ is an uncertain quantity. Much depends on the 
virulence of the organisms occupying the nodules. These bac- 

* Smith, C. D., and Robinson, F. W., Influence of Nodules on the Soots 
upon the Composition of Soybean and Cowpea; Mich. Agr. Exp. Sta., 
Bui. 224, 1905. 

Hopkins, C. G., Alfalfa on Illinois Soil; Til. Agr. Exp. Sta., Bill. 76, 
1902. 

Hopkins, C. G., Nitrogen Bacteria and Legumes; 111. Agr. Exp. Sta., 
Bui. 94, 1904. 

Shutt, F. T., The Nitrogen Enrichment of Soils through the Growth 
of Legumes; Canadian Dept. Agr., Rept. Centr. Exp. Farms, 1905, pp. 
127-132. 



540 NATURE AND PROPERTIES OF SOILS 

teria are in turn much influenced by plant and soil conditions, 
such as amount of organic matter, presence of nitrates, acidity 
and the like. Hopkins ^ estimates that about one-third of the 
nitrogen in a normal innoculated legume comes from the soil 
and two-thirds from the air. He also considers that one-third 
of the nitrogen exists in the roots. 

Both of these assumptions are questionable and at best 
tentative. The amount of nitrogen fixed by legume organisms 
is extremely variable, probably more so than that assimilated 
by the azotobacter and allied groups. Again the percentage 
of the nitrogen held in the roots of legumes is by no means 
the same for all species. The amount varies within the species 
with age, degree of maturity and, season. The Delaware in- 
vestigations - show that the proportion of the total nitrogen 
of the plant occurring in the roots may be as low as 6 per cent, 
in case of cowpeas and as high in the roots of alfalfa as 42 
per cent. A range from 6 to 28 per cent, of the total nitrogen 
of crimson clover was noted in the roots under different condi- 
tions. 

According to Hopkins, the nitrogen found in the tops of 
legumes will be a rough measure of the nitrogen fixed by the 
nodule organisms. When the crop is turned under, this will 
represent the gain to the soil. If the preceding assumption 
is correct, red clover turned under would actually add about 
50 pounds of nitrogen for every ton of air-dry substance util- 
ized, alfalfa about 50, cowpeas 43, and soybeans 53 pounds. 
These figures, even though they may be far from correct, at 
least give some idea of the possible addition of nitrogen by 
green-manuring practices, and show how the soil may be en- 
riched by such management. As in the case of farm manures, 
the indirect effects of such a procedure on the physical and 
bacteriological properties of the soil may over-ride the direct 

^ Hopkins, C. G., Soil Fertility and Permanent Agriculture, p. 223 ; 
Boston, 1910. 

^ Penny, C. L., The Growth of Crimson Clover; Del. Agr. Exp. Sta., 
Bui. 67, 1905. 



GREEN-MANURES 541 

influences, lessening the advantage that legumes as green- 
manures are supposed to have over non-legumes, due to their 
ability to use atmospheric nitrogen. 

311. Green-manures as cover-crops. — When green-ma- 
nures are seeded in the late summer or early fall, they func- 
tion as cover-crops and may have rather important influences 
aside from their effects when turned under. Their greatest 
influence seems to be on the nitrate content of the soil. Nitri- 
fication is usually checked,^ a disappearance of nitrates gen- 
erally following. This reduction in the amount of nitrates 
probably occurs because of a retardation of nitrification ac- 
companied by a stimulation of biological utilization of the 
nitrates. Such an effect is important in conserving the soil 
nitrogen and is of particular value in orchards,- as it hastens 
the maturity of the new growth. At Cornell University, 
green-manures were seeded in July and plowed under in the 
following spring. Nitrate determinations were made on the 
soil in July and in October. The figures are five-year aver- 
ages. (See Table CXXIII, page 542.) 

312. The decay of green-manure. — When a green-crop 
is turned under, the process of its decay is the same as that 
of any plant tissue that becomes a part of the soil body. The 
organisms that are active are those common to the soil, to- 
gether with such bacteria as are carried into the soil on the 
turned-under crop. The decomposition that results is prob- 
ably both aerobic and anaerobic in nature, carbon dioxide be- 
ing given off continuously. When proper decay has occurred, 
end products should result which can be utilized as nutrients, 

1 Wright, E. C, The Influence of Certain Organic MateriaU upon the 
Transformation of Soil Nitrogen; Amer. Soc. Agron., Vol. 7, pp. 193- 
208, 1915. 

Martin, T. L., The Decomposition of Green Manures at Different Stages 
of Growth; Thesis for degree of Doctor of Philosophy, Cornell University, 
1919. 

^ Lyon, T. L., The Formation of Nitrates in Soil Under Grass; 
Proc. West. N. Y. Hort. Soc, pp. 82-87, Jan., 1915. 

Lyon, T. L., Eelation of Certain. Cover Crops to the Formation of 
Nitrates in Soil; Proc West. N. Y. Hort. Soc, pp. 32-34, Jan., 1917. 



542 NATURE AND PROPERTIES OF SOILS 



Table CXXIII 

effect of various crops on the nitrate nitrogen of the 
soil during october, 1916-1920.^ 



Green-Manuring Crop 



Rye 

Oats 

Vetch 

Peas 

Rye and vetch 
Rye and peas. 
Sod 



Nitrates in the 

Soil in October. 

Eye Taken as 

100 




Percentage Ee- 

duction of 

Nitrates in 

October Compared 

WITH July 



37 
44 
57 
10 

58 

58 





The intermediate compounds that are formed should yield 
an organic matter carrying a black pigment, should readily 
split up into simple compounds, and should be in general 
beneficial, both directly and indirectly, to plant growth. 
Plenty of moisture is essential when green-manures are de- 
caying, not only to hasten the transformation itself but that 
the normal soil processes may not be interrupted by a lack 
of water. The caution with which green-manures must be 
utilized in semi-arid regions arises because of the drying influ- 
ences of rapid decay and the danger of filling the soil with 
undecomposed plant residues. Even in humid regions, green- 
manures may be detrimental if dry weather sets in before a 
major portion of the decay processes is completed. 

As plant tissue decays in the soil, there seem to be two 
general groups of forces at work which produce three distinct 
stages of organic destruction.^ In the first stage, humus pro- 

^ Unpublished data. Dept. Soils. Cornell University. 

- Martin, T. L., The Decomposition of Green-Manures at Different 
Stages of Growth; Thesis for degree of Doctor of Philosophy, Cornell 
University, 1919. 



GREEN-MANURES 543 

duction is dominant and the amount of the humous materials 
increases. In the second stage, humus production and humus 
destruction are more or less balanced, while in the third stage 
humus destruction is in the ascendant. The amount of humus 
is on the decrease in the latter stage. The length of these 
stages will vary with the season, with soil conditions,' and 
with the character of the crop turned under. Obviously, the 
influence of decomposing green-manure on the chemical and 
biological activities of the soil will vary as the decay cycle 
progresses. In general, over one-half of the organic matter 
of the average green-manure disappears during the first nine 
months after application. 

313. Influence of decaying green-manure. — In the first 
stage of decay, which should be a rapid one, many complex 
compounds are generated along with carbon dioxide and other 
simple products. The complex materials, which result partly 
from protein decomposition and partly from the breaking 
down of easily attacked carbohydrates, may be harmful to 
ordinary crops. Germinating seeds and young plants are 
especially susceptible, and detrimental influences are some- 
times noticed immediately after the turning under of a green- 
manure. Fred ^ found that the germination of oily seeds, 
such as cotton and soybean, was much reduced. Starchy 
seeds, such as maize, oats, and wheat, were little affected. The 
germination of flax, hemp, mustard, and clover was some- 
what reduced. An actual contact of the seed with the de- 
caying material was usually necessary for serious damage. 
The detrimental influence always occurred during the first 
two or three weeks after the green-crop was turned under. 
Obviously the more succulent the crop, the shorter will this 
period be. 

^Eussell, E. J., and Appleyard, A., The Influence of Soil Conditions 
on the Decomposition of Organic Matter in the Soil; Jour. Agr. Sci,, 
Vol. VIII, Part 3, pp. 385-417, 1917. 

*Fred, E. B., Eelation of Green Manure to the Failure of Certain 
Seedlings; Jour. Agr. Ees., Vol. V, No. 25, pp. 1161-1176, Mar., 1916. 



544 NATURE AND PROPERTIES OF SOILS 

Not only do the products of the first stage of decay influ- 
ence the crop growing on the soil, but they affect the biological 
activities as well/ Nitrification in particular seems to be in- 
fluenced, as nitrates do not begin to appear until the process 
of humification is well advanced. Nitrification, however, is 
probably not entirely suppressed as it is possible for soil or- 
ganisms to use up the nitrates as rapidly as they are formed. 



If 

3., 

IK 



^N / 




III ^*- 


M 



z 

o 

CD 

tz 

u 



TIME AFTER APPLICATION 



Fig. 64. — Diagram illustrating the three stages in the decay of a 
green-manure. I, humus production dominant; II, a balance be- 
tween humus production and destruction; III, humus destruction 
dominant. A depression in nitrate accumulation generally occurs 
in stage I followed by an increase. (After Martin.) 

As the humus destruction gradually dominates over humus 
production, the end products of the decay become prominent. 
The complex proteid decomposition is practically completed 
and cellulose destruction is slowly progressing. Of the sim- 
ple nutritive products, the nitrates are of particular impor- 
tance. In fact, they have been chosen by a number of in- 



^ Briscoe, C. F., and Harned, H. H., Bacterial Effects of Green 
Manures; Miss. Agr. Exp. Sta., Bui. 168, Jan. 1915. 

Hutchinson, H. B., The Influence of Plant Residues on Nitrification 
and on Losses of Nitrates in Soil; Jour. Agr. Sci., Vol. IX, Part 1, 
pp. 92-111, Aug. 1918. 



GREEN-MANURES 545 

vestigators ^ as a measure of humification, since a favorable 
environment for nitrification probably does not occur until 
the more rapid decomposition processes are completed. In 
general, the more rapid the decay of the green-manure, the 
sooner will nitrification be active again. 

Besides affecting the bacterial activity of the soil, the de- 
caying green-crop influences the solubility of the soil min- 
erals. Jensen - found that the addition of 3 per cent, of 
green-manure raised the solubility of lime and phosphoric 
acid 30 to 100 per cent. This was over and above the mineral 
constituents which came directly from the decomposing green- 
crop. Magnesium and iron were also markedly influenced. 

314. Crops suitable for green-manures. — An ideal green- 
manuring crop should possess three characteristics: rapid 
gro"«i;h, abundant and succulent tops, and the ability to grow 
well on poor soils. The more rapid the growth, the greater 
the chance of economically using such a crop as a means of 
soil improvement. The higher the moisture content of the 
crop, the more rapid the decay and the more quickly are bene- 
fits obtained. As the need of organic matter is especially 
urgent on poor land, a hardy crop has great advantages. 

The crops that may be utilized as green-manures are usually 

^Hutchinson, C. M., and Milligan, S., Green-Manuring Experiments, 
1912 and 1913. India Agr. Kes. Inst. Bui. 40, Pusa, India, 1914. 

Mavnard, L. A., The Decomposition of Siceet Clover as a Green- 
Manure under Greenhouse Conditions ; Cornell Agr. Exp. Sta., Bui. No. 
394, 1917. 

Martin, T. L., The Decomposition of Green-Manures at Different 
Stages of Growth; Thesis for degree of Doctor of Philosophy, Cornell 
University, 1919. 

^ Jensen, C. A., Effect of Decomposing Organic Matter on, the Solu- 
bility of Certain Inorganic Constituents of the Soil; .Jour. Agr. Res., 
Vol. IX, No. 8, pp. 253-268, May 1917. 

See also, Snyder, H., Humus as a Factor in Soil Fertility; Minn. Agr. 
Exp. Sta., Bui. 41, 1895; and Production of Humus from Manures; 
Minn. Agr. Exp. Sta., Bui. 53, 1897. 

Hopkins, C. G., and Aunier, J. P., Potassium from the Soil; 111. Agr. 
Exp. Sta., Bui. 182, 1915. 

Hopkins, C. G., and Whiting, A. L., Soil Bacteriology and Phosphates; 
111. Agr. Exp. Sta., Bui. 190, 1916. 



546 



NATURE AND PROPERTIES OF SOILS 



grouped under two heads, legumes and non-legumes. Some 
of the common green-manures are as follows: 





LEGUMES 


NON-LEGUMES 


Annual 




Biennial 




Cowpea 




' Red clover 


Rye 


Soybean 




White clover 


Oats 


Peanut 




Alsike clover 


Mustard 


Vetch 




Alfalfa 


Mangels 


Canada field 


pea 


Sweet clover 


Rape 


Velvet bean 






Buckwheat 


Crimson clover 






Hairy vetch 









When other conditions are equal, it is of course always bet- 
ter to choose a leguminous green-manure in preference to a 
non-leguminous one, because of the nitrogen that may be 
added to the soil. However, it is so often difficult to obtain 
a catch of some of the legumes that it is poor management to 
turn the stand under until after a number of years. Again, 
the seed of many legumes is very expensive, almost prohibit- 
ing their use as green-manures. Among the legumes most 
commonly grown as green-manures, cowpeas, soybeans, and 
peanuts may be named. Many of the other legumes do not so 
fit into the common rotations as to be turned under conven- 
iently as a green-manure. 

For the reasons already cited, the non-legumes have, in 
many cases, proved the more popular and economic as green- 
manures. Rye and oats are much used because of their rapid, 
abundant, and succulent growth and because they may be 
accommodated to almost any rotation. They are hardy and 
will start in almost any kind of a seed-bed. They are thus 
extremely valuable on poor soils. Often the value of such a 
green-manure as oats is greatly increased by sowing peas with 
it. The advantages of a legume and a non-legume are thus 
combined. 

It has already been shown that the nitrate production in a 



GREEN-MANURES 



547 



soil may be used as a rough measure of the rate of decay of 
green-manures. Admitting such a criterion, certain data from 
Cornell University become particularly interesting. In a 
five-year continuous test, green-manuring crops were seeded 
in July and plowed under in the early part of the succeeding 
Ma.y. The nitrate content of the soil was determined at a 
number of times during the spring, summer, and fall. A de- 
crease in nitrates always occurred in the autumn, while an 
increase began soon after the crops were turned under in the 
spring. In the following table the rye crop is taken as 100 in 
both October and July : 

Table CXXIV 

relative influence of green-manltres on the 
accumulation of soil nitrates.^ 



Green-Manuke 



Nitrates in July, 
Soil Fallow Since 

May 1. 
Rye Taken as 100 



Nitrates in Oct., 
Soil Under Crop 

Since July. 
Rye Taken as 100 



Rye 

Oats 

Vet.'h 

Peas 

Rye and vetch 
Rye and peas. 




100 
73 
73 
83 
74 
75 



It is immediately apparent that the succulent rye and vetch 
that survive the winter give better results, as far as nitrate 
production is concerned, than the dry and dead oats and peas. 
This shows clearly the value of succulence and the necessity 
of turning under a crop partially matured.^ The advantage 
of the legumes over the non-legumes is not hard to explain. 



* Unpublished data. Dept. Soils, Cornell University. 

^ Martin, T. L., The Decompvsition of Green Manures at Different 
Stages of Growth; Thesis for the Degree of Doctor of Philosophy, 
Cornell University, 1919. 



548 NATURE AND PROPERTIES OF SOILS 

The combination of rye and vetch, both of course in a succu- 
lent condition, seems especially efficacious. Sod as a green- 
manure always appears more or less at a disadvantage. 

315. The use of green-manures. — The indiscriminate 
use of green-manures is of course never to be advised, as the 
soil may be injured thereby and the normal rotation much 
interfered with. When soils are poor in nitrogen and organic 
matter, they are very often in poor tilth. This is true whether 
the texture of the soil be fine or coarse. The turning-under 
of green-crops must be judicious, however, in order that the 
soil may not be clogged with undecayed matter. Once or twice 
in a I'otation is usually enough for such treatments. Proper 
drainage must always be provided. In regions where the rain- 
fall is scanty, great caution must be observed in the handling 
of green-manures. The available moisture that should go to 
the succeeding crop may be used in the process of decay, and 
the soil left light and open, due to an excess of undecomposed 
plant tissue. In western United States, it is still a question 
whether green-manures have any advantage over summer 
fallowing. 

It is generally best to turn under green-crops when their 
succulence is near the maximum and yet at a time when 
abundant tops have been produced. This occurs at about the 
half mature stage. A large quantity of water is carried into 
the soil when the crop is at this stage, and the draft on the 
original soil-moisture is less. Again, the succulence encour- 
ages a rapid and more or less complete decay, with the maxi- 
mum production of humus and other products. The plowing 
should be done, if possible, at a season when a plentiful supply 
of rain occurs. The effectiveness of the manuring is thereby 
much enhanced. At Cornell University various green-manures 
were seeded in the summer and plowed under that fall or the 
next spring. The experiment was continuous for three years, 
the nitrates being determined in the soil each year in April 
and in June. The results are as given on the next page. 



GREEN-MANURES 



549 



Table CXXV 

influence of the time of turning-undeb of green-manures 
on the nitrate accumulation in the soil.^ 



Crop 



Rye, fall plowed 

Rye, spring" plowed .... 

Oats, fall plowed 

Oats, spring plowed . . . , 

Vetch, fall plowed 

Vetch, spring plowed. . 

Average, fall plowed. . . 
Average, spring plowed 



Paets Per Million of Nitrates 



In April Just 

Before the 
Spring Plowing 


In June, Soil 

Fallowed Since 

Plowing 


58 
53 


57 
67 


61 
36 


42 
50 


79 
41 


45 

67 


66 
43 


48 
61 



It is apparent that the decay of the green-manuring crop 
is hastened by fall plowing, as the nitrates in every case are 
higher in April on land so handled. In June, however, the 
nitrate accumulation has passed its highest point in the fall- 
plowed soil, leaving the spring-plowed plats, where the decay 
was initiated later, in the ascendancy. The table also shows 
the advantage that a legume has over a non-legume in causing 
nitrate accumulation. Oats fall-plowed appear about on an 
equality with rye. Spring plowing, since the oats are then 
dry and dead, gives the rye a marked advantage. All of the 
points above noted have a very practical field application. 

In turning under green-manures, the furrow slice should 
not be thrown over flat, since the green-crop is then deposited 
as a continuous layer between the surface soil and the sub- 
soil. Capillary movement is thus impeded until a more or 

* Unpublished data, Dept. Soils, Cornell University. 



550 NATURE AND PROPERTIES OF SOILS 

less complete delay has occurred, and the succeeding crop 
may suffer from lack of moisture. The furrow ordinarily 
should be turned only partly over, and thrown against and 
on its neighbor. The green-manure is then distributed evenly 
from the surface downward to the bottom of the furrow. 
When decomposition occurs, the resulting materials are evenly 
mixed with the whole furrow slice. Moreover, this method of 
plowing does not interfere with the capillary movements of 
water, and in actual practice is a great aid in drainage and 
aeration. 

316. Green-manure and lime. — The decay of organic 
matter in the soil is always accompanied by the production of 
organic acids of various kinds. The greater the succulence 
of the material, the more rapid is the accumulation of such 
products. In spite of this, however, the effect of a green- 
manure is to decrease the acidity rather than increase ^ it and 
later greatly to stimulate nitrification even if the soil origi- 
nally was quite acid. The decrease in lime requirement may 
be due to the liberation of mineral constituents from the de- 
caying organic matter and to the effect of the decomposition 
on the inorganic constituents of the soil. 

The ultimate influence of green-manure on acidity is some- 
what in doubt. The bulk of the evidence available seems to 
indicate that decaying organic matter, if it has any effect, ulti- 
mately tends to decrease rather than increase the lime re- 
quirement of the soil.^ Nevertheless, plenty of active calcium 
should be in the soil, since it promotes the decay of the plant 
tissue added and seems to control to a certain extent the pres- 
ence of toxic materials. Lime may be added to the green- 
manure seeding and be turned under with that crop. The 

^ White, J. W., Soil Acidity as Influenced by Green Manures; Jour. 
Agr. Res., Vol. XIII, No. 3, pp. 171-197, April, 1918. 

" Hill, H. H., A Comparison of Methods for Determining Soil Acidity 
and a Study of the Effects of Green Manures on Soil Acidity; Va. 
Poly. Inst., Tech. Bui. 19, April 1919. 

Ames, J. W., and Schollenberger, C. J., Liming and Lime Eequire- 
ment of Soils; Ohio Agr. Exp. Sta., Bui. 306, pp. 381-383, Dec. 1916.' 



GREEN-MANURES 



551 



amendment would thus be in very close contact with the de- 
caying vegetable tissue. Ordinarily, however, the application 
of lime at some point in the rotation is sufficient. 

Lime, besides its capacity to alleviate toxic residues, tends 
to hasten organic deeay.^ This is a very important function 
as the first stage of decomposition, during which soil and plant 
activities may under certain conditions be detrimentally af- 
fected, is markedly shortened. Such a promotion is indicated 
in a green-manuring experiment at Cornell University. The 
green-manures were seeded in the fall under two treatments, 
limed and unlimed. The parts per million of nitrates in the 
soil are given for two dates on the year succeeding, the green- 
manures having been plowed under either in the fall or early 
spring. The data are average^ of three years. 

Table CXXVI 

influence of lime on the nitrate accumulation in a soil 
receiving various green-manures." 





Parts Per Million of Nitrates 




April 


June 


Rye, no lime 


66 
45 

53 

45 

77 
43 

65 
44 


53 


Rye, limed 


71 


Oats, no lime 

Oats, limed 

Vetch, no lime 


43 

50 

52 


Vetch, limed 


63 


Average, no lime 


49 


Average, limed 


61 







^ Lemmermann, O., et al., Untersucliunr/ iiher die zerzetzung der Kohlen- 
stoff Verbindungen Verscheidener Organischen Substanzen im Boden 
SpezieUe unter dem einfluss der Kalk ; Landw. Jahrb., Bd. 41, S. 216- 
257, 1911. 

^ Unpublished data. Dept. Soils, Cornell University. 



552 NATURE AND PROPERTIES OF SOILS 

The effect of lime on nitrification is very noticeable in June. 
In April the no-lime plats are higher in accumulated nitrates, 
due to the lesser growth of the green-manuring crop. 

317. Practical utilization of green-maimres. — Green- 
manures seem to have their greatest value where a permanent 
instead of a rotation pasture is used, where a long cycle rota- 
tion of grain is practiced, or where little or no manure is 
available. The experimental data bearing on the use of green- 
manures seems to indicate that such a practice is productive 
of larger crop yields. The following data from Nappan, Nova 
Scotia, is from one of the more reliable and conclusive experi- 
ments. A catch-crop of clover in the grain was turned under 
for grain the following year. The figures are for 1905, the 
third year of the test. 

Table CXXVII 

yield of wheat, oats and barley in bushels to the acre 

on the nappan farm in 1905 on plats cropped 

continuously to grain.^ 



Treatment 


Wheat 


Oats 


Barley 


No green-manure 

Clover catch-crop 


34.3 
40.0 


41.2 
55.3 


32.7 
37.9 







The use of a green-manure is often determined by the char- 
acter of the rotation. Very often it is somewhat of a problem 
as to when, in an ordinary rotation, a green-manure may be 
introduced so that it may fit in well with the crops. In a 
rotation of maize or potatoes, oats, wheat, and two years of 
hay, a green-manure might be introduced after the corn or 
potatoes. This would not be a very good practice, however, as 
a cultivated crop usually should follow a green-manure in 
order to facilitate decomposition and decay. In such a rota- 
tion, the plowing-under of the hay stubble is really a form 

^ Ottawa Exp. Farms Kept., 1905, p. 284. 



GREEN-MANURES 553 

of green-manuring, there being a considerable accumulation 
of stubble and aftermath on the soil. When a rotation of 
this kind is used, it is better either to supply organic matter 
in other ways, or to alter or break the rotation in such a man- 
ner as to admit of a more advantageous use of green-crops. 

Where trucking crops are raised and no very definite rota- 
tice is adhered to, green-manuring is easier. It is especially 
facilitated when cover-crops are grown, as in orchards. Soil- 
ing operations also favor the easy and profitable use of green- 
manures. In general, it may be said that the organic matter 
obtained from such a source should be supplemented by farm- 
yard manures where possible. A better balanced and richer 
soil organic matter is more likely to result. 



CHAPTER XXVI 
THE MAINTENANCE OF SOIL FERTILITY ^ 

The maintenance of a profitable and continuous soil pro- 
ductivity is an intricate problem, since many variable factors 
are involved. Weather conditions, moisture relations, soil or- 
ganic matter and tilth, plant diseases, soil reaction, and avail- 
able nutrients are only a few of the influences that function 
continuously throughout the growing season. No scheme of 
soil management and crop production is perfect, even though 
it is fairly profitable. Except in special cases, every system is 
open to improvement and modification as soil and plant 
knowledge increases. 

The sources of knowledge regarding the profitable growing 
of plants are numerous. Much data have arisen from expe- 
rience and observation, much are empirical, while some are 
confessedly conjectural. In spite of the large amount of 
scientific information available regarding the soil and its 
plant relationships, practical experience has contributed more 
towards a profitable and continuous soil productivity. Soil 
survey classification and mapping have contributed some- 
thing. Field tests, both practical and technical, have added 
to such information, while laboratory and greenhouse experi- 
ments, although often arbitrary and artificial, are by no 
means unimportant. These latter contributions, however, 
always need practical confirmation under typical field con- 
ditions over a period of years. 

318. Loss of plant nutrients from the soil. — A consid- 
eration of the principles governing the rational management 

^ Fertility is here used in the sense of continuous productivity. 

554 



THE MAINTENANCE OF SOIL FERTILITY 555 

of a soil is obviously impossible unless some knowledge is at 
hand regarding: the losses and additions which a soil sustains 
in the course of a definite rotation. Fortunately, some fairly 
reliable data have already been presented regarding the re- 
moval of soil constituents under controlled conditions. The 
Cornell lysimeter tanks, bearing a rotation of maize, oats, 
wheat, and two years of hay, offer very satisfactory informa- 
tion (paragraphs 95 and 163). The losses covering a ten-year 
period are expressed in pounds to the acre a year. The soil is 
a Dunkirk silty clay loam. 

While such figures are probably open to considerable error 
and obviously would not apply with any degree of accuracy 
to a light soil, they indicate in a general way the magnitude 
and order of the losses that may be expected from such a soil 
under the conditions specified. 

Table CXXVIII 

losses from a dunkirk silty clay loam soil expressed in 

pounds to the acre a year over a ten- year period. 

rotation: maize, oats, wheat and two years 

hay. cornell lysimeter tanks. 



Source of Loss 


N 


P.O. 


K^O 


CaO 


SOs 


Drainage (par. 163) .... 
Cropping (par. 163) .... 
Atmosphere (pars. 

220 and 233)^ 


7.3 
70.5 

? 


trace 
43.5 


68.7 
105.4 


345.9 
24.3 


108.5 
41.0 


Total 


77.8 


43.5 


174.1 


370.2 


149.5 



The organic carbon in this soil over the ten-year period was 
reduced at the rate of approximately 1 per cent, a year.- This 
is equivalent to a reduction in organic matter of about 1200 

* The largest loss of carbon is probably to the atmosphere as carbon 
dioxide. The other avenue of loss is in the drainage water. 

" Lipman and Blair report a reduction of organic carbon of .74 per 
cent, a year over a period of ten years on Sassafrass loam in New 



556 NATURE AND PROPERTIES OF SOILS 

pounds each year to the acre-four feet. It is evident, there- 
fore, that the losses sustained by the average soil fall most 
heavily on the organic constituents, a condition often ignored 
in practical soil management. The removal of calcium oxide is 
also very large, being equivalent to a loss of 661 pounds of 
calcium carbonate an acre a year. Although losses of sulfur 
trioxide and phosphoric acid are smaller than that of the 
potash, they are far more important, since there is very com- 
monly one hundred times more potash in a soil than of the 
other two constituents combined. The magnitude of the loss 
of a soil constituent is never a safe measure of its importance. 
The removal of nitrogen is equivalent to over 500 pounds of 
commercial sodium nitrate and consequently is also a loss of no 
small consideration. 

319. Additions of nutrients to the soil. — The figures 
presented above are based on reliable experimental data. Un- 
fortunately the information regarding the additions which 
normally occur to a soil under any particular rotation are by 
no means so exact. Certain assumptions and estimates, often 
of questionable validity, must be admitted in order that a 
complete survey may be possible. Table CXXIX sets forth 
the additions which the Dunkirk clay loam of the Cornell lysi- 
meters may reasonably be expected to receive each year when 
cropped to a five-year rotation of maize, oats, wheat, and two 
years hay. The data are expressed in pounds to the acre a 
year. (See Table CXXIX, page 557.) 

The additions listed above are not the only avenues open 
for important acquisitions. The crops removed may be fed to 
animals and the manure returned to the land. Moreover, the 
utilization of a green-manure is also possible. Below will be 
found the additions that may reasonably be expected from the 

Jersey. The rotation was maize, oats, wheat, and two years hay. No 
lime was added. 

Lipman, J. G., and Blair, A. W., The Lime Factor in Permanent 
Soil Improvement. I. Rotations Without Legumes; Soil Sci., Vol. 
IX, No. 2, p. 87, 1921. 



THE MAINTENANCE OF SOIL FERTILITY 557 



Table CXXIX 

estimated additions that might occur to a soil under a 

rotation of maize, oats, wheat, and two years hay. 

expressed in pounds to the acre a year. 



Source of Addition 


N 


P.O. 


K^O 


CaO 


SO3 


Rain-water (pars. 236 and 264) 
Free fixation by soil organisms 

(par. 238) 

Crop-roots and residues ^ 


12.5 
25.0 








65.0 


Total 


37.5 






65.0 



use of farm manure and a green-manure on the soil in question. 
The green-manure is leguminous and is applied once during 
the five-year rotation. 

Table CXXX 

further additions that might be made to the five-year 

rotation on dunkirk silty clay loam, expressed in 

pounds to the acre a year. 



Additions 


N 


P2O, 


K,0 


CaO 


SO3 


Organic 

Matter 


Farm manure - 

Leguminous green- 
manure ^ 


21.1 
20.0 


21.7 


31.6 


7.3 


12.4 


1000 
600 






Total 


41.1 


21.7 


31.6 


7.3 


12.4 


1600 







^ Important because of the additions of organic matter that occurs 
thereby. 

^ It is estimated that of the crops removed and fed or used as bedding, 
only 30 per cent, of the N, KjO, CaO and SO3, 50 per cent, of the PjOg 
and 25 per cent, of the organic matter reach the soil as farm manure (par. 
294). The crops removed carried about 4000 pounds of organic matter 
to the acre. 

^ The green-manure is estimated as 4000 pounds of air-dry matter 
carrying 100 pounds of nitrogen, which is considered as fixed from the 
air. This should yield 3000 pounds of soil organic matter. 



558 NATURE AND PROPERTIES OF SOILS 

320. The balance sheet. — For convenience of compari- 
son, the data previously presented are drawn together in a 
single table and presented below as pounds to the acre an- 
nually. These figures are considered as relating to the Dun- 
kirk silty clay loam carrying a five-year rotation of maize, 
oats, wheat, and two years hay. It must always be remem- 
bered that such data are specifically applicable to only one 
soil. Nevertheless the practical deductions that may be drawn 
are of wider scope. 

Table CXXXI 

summary table of losses and additions that might occub 
to dunkirk silty clay loam under a five-year rota- 
tion, expressed in pounds to an acre a year. 



Conditions 



Reductions when farm 
manure and green ma- 
nure are not used ^. . . . 

Additions from farm ma 
nure 

Additions from farm ma 
nure and green-manure 

Additions using green- 
manure 



N 


P2O5 


KjO 


CaO 


SO3 


40.3 


43.5 


174.1 


370.2 


84.5 


21.1 


21.7 


31.6 


7.3 


12.4 


41.1 


21.7 


31.6 


7.3 


12.4 


20.0 


— 


— 


— 


— 



Organic 
Matter 



1200 

1000 

1600 

600 



It is immediately apparent that when farm manure and 
green-crops are not utilized, a notable decrease occurs in every 
constituent cited. Such a system of soil management must 
reduce the productivity of the soil very quickly and 
certainly is not a rational scheme of soil and crop adjustment. 
Nevertheless, it is the condition under which much of the 
arable land is producing crops today. 

When farm manure is utilized, even allowing for a large 

* Obtained by subtracting the natural additions from the rormal 
losses. 



THE MAINTENANCE OF SOIL FERTILITY 059 

waste in its production and handling, the organic matter is 
almost maintained and the loss of nitrogen is met to some ex- 
tent. Under such a system, the addition of nitrogen and of 
mineral constituents is a problem, although sCme attention 
should be paid to the soil organic matter. Liming will be 
necessary ultimately if not immediately, while the addition 
of phosphoric acid obviously will some day be profitable. 
If acid phosphate is utilized at a normal rate, the sulfur 
losses that occur should be very nearly counterbalanced. 
Potash, especially as the soil under consideration is a clay 
loam, will no doubt be available for a long period if the 
organic matter is adequately maintained. 

The use of a green-manure once in the rotation in addition 
to the farm manure Avill adequately care for the soil or- 
ganic matter and reduce the nitrogen problem to a minor 
position. 

When animal products are relatively high in price and 
crop values are low, stock farming will be advisable and a sj^s- 
tem whereby considerable farm manure will be available may 
be followed. It has already been indicated that under such 
conditions the organic matter, and to a lesser degree the nitro- 
gen content of the soil, may adequately be maintained espe- 
cially if a green-manure is used once in the rotation. Where 
grain farming is necessary, reliance must be placed almost 
wholly on green-manures for the upkeep of the soil organic 
matter, especial care being given to the full utilization of crop 
residues. According to the data presented in Table CXXXI, 
such a system, as far as the nitrogen and organic matter are 
concerned, could be made about as satisfactory as where farm 
manure is available and has the possibility and advantage of 
considerable expansion. Grain farming makes necessary, 
however, a more intensive and careful use of mineral constitu- 
ents. Liming and commercial fertilizers will, therefore, fig- 
ure somewhat more prominently in grain-growing than where 
dairying or stock-raising are practiced. 



560 NATURE AND PROPERTIES OF SOILS 

321. The maintenance of soil fertility.^ — The practical 
management of a soil, whereby profitable crops may be grown 
without materially reducing the fertility of the land rests 
on five fundamental principles. The basic factors are: (1) 
drainage, (2) tillage, (3) organic matter, (4) lime, and (5) 
fertilizers. Obviously, the removal of excess water depends 
on adequate drainage, while aeration and all of the activities 
that attend it rests both on drainage and tillage. The upkeep 
of the soil organic matter by the use of crop roots and resi- 
dues, by farm manure, and by the turning under of green- 
crops has already been emphasized as fundamental to con- 
tinuous productivity. 

These factors are by no means the whole program of ra- 
tional soil management. Artificial additions must be made. 
Of these lime is of vital importance. Calcium and magnesium 
are lost from the soil in such large amounts that outside 
sources must be drawn on. Every arable soil will ultimately 
come to the point where liming will be profitable. Finally, the 
judicious use of commercial fertilizers must receive attention. 
The addition of phosphoric acid will probably be the first 
fertilizer element to be considered seriously, especially in gen- 
eral farming. Under special conditions of soil and crop, nitro- 
gen and potash will also be a part of the program. The adap- 
tation of crops in suitable rotation to climate and soil, with 
adequate attention to the factors emphasized above, are the 
prime essentials of a paying system of permanent soil pro- 
ductivity. 

^ Hartwell, B. L., and Damon, S. C, Six Years' Experience in Im- 
proving a Light Unproductive Soil; Jour. Amer, Soc. Agron., Vol. 13, 
No. 1, pp. 37-41, 1921. 

Lipmau, J. G., and Blair, A. W., Tiie Lime Factor in Permanent 
Soil Improvement. I. notations without Legumes. II. Botations with 
Legumes; Soil Sci., Vol, IX, No. 2, pp. 83-114, 1921. 



INDEX OF AUTHORS 



Aarnio, B., 134. 

Abbott, J. B., 347. 

Aberson, J. H., 252. 

Agee, A., 362. 

Ageton, C. U., 376. 

Aikman, C. M., 504. 

Allen, E. R., 424. 

Allison, F. E., 387. 

Alway, F. J., 43, 44, 63, 115, 118, 119, 

120, 155, 163, 160, 195, 198, 

199, 221. 
Ames, J. W., 58, 406, 470, 499, 550. 
Ammon, Georg, 156. 
Appiani, G., 73. 
Appleyard, A., 158, 248, 252, 253, 257, 

273, 543. 
Ashby, S. F., 424. 
Ashley, H. E., 132, 134, 137. 
Atterburg, A., 68, 140, 141, 187. 
Averltt, S. D., 118. 
Aunier, J. P., 545. 

Bancroft, W. B., 127, 129. 

Barker, P. B., 221. 

Barlow, J. T., 358. 

Barrett Company, The, 449. 

Bauniann, A., 106. 

Beattie, J. H., 351, 520, 521. 

Beaumont, A. B., 134, 157. 

Beavers, J. C, 499. 

Bennett, H. H., 38, 50, 63, 118. 

Bernard, A., 467. 

Bertholot, M., 431. 

Bertrand, G., 466. 

Bishop, E. S., 120. 

Bizzell, J. A., 179, 207, 251, 252, 284, 

422, 43G. 437. 
Blair, A. W., 307, 354, 356, 381, 556, 

560. 
Blanck, E., 478. 
Bogue, R. H., 267. 
BoUey, H. L., 397. 
Boltz, G. E., 406, 470. 



Boullanger, E., 466, 467. 

Bouyoucos, G. J., 153, 154, 155, 159, 
160, 171, 175, 182, 196, 223, 
228, 232, 235, 239, 259, 277, 
280, 281, 286, 287, 291, 356. 

Bradley, O. E., 380. 

Breazeale, J. F., 113, 331, 381. 

Brcnchley, W. E., 284, 287. 

Briggs, L. J., 67, 113, 156, 168, 171, 
172, 188, 190, 195, 196, 197, 
277, 278, 380. 

Bright, J. W., 505. 

Briscoe, C. F., 544. 

Brodie, D. A., 499. 

Bronet, G., 267. 

Brooks, W. P., 461, 522. 

Broughton, L. B., 377. 

Brown, R E., Ill, 422. 

Brown, C. F., 211, 340. 

Brown, P. E., 44, 362, 388, 392, 405, 
406, 421, 424. 

Bryan, H., 71. 

Buckingham, E., 182, 260. 

Buckman, H. O., 29. 

Buddin, AV., 414. 

Bunger, H., 186. 

Burd, J. S., 280, 322, 325. 

Burdick, R. T., 499. 

Burr, W. W., 194, 221. 

Burton, E. F., 127, 129. 

Caldwell, J. S., 195. 

Call, L. E., 220, 221. 

Cameron, F. K., 113, 141, 283. 

Carr, R. H., 116, 143. 

Carrero, P. L., 299. 

Carter, E. G., 392, 393, 421, 464. 

Gates, J. S., 221. 

Chamberlain, T. C, 57. 

Chase, L. W., 144. 

Christrnsen, H. R., 354. 

Clarke, F. W., 4, 13. 

Clarke, V. L., 155, 198. 



561 



562 



INDEX OF AUTHORS 



Coffman, W. B., 190. 

Coleman, D. A., 387, 388. 

Coleman, L. C, 420. 

Collins, S. H., 442. 

Comber, N. M., 360. 

Conn, H. J., 388, 389, 505. 

Conn, H. W., 384. 

Conner, S. D., 295, 328, 347, 349, 351, 

457, 461. 
Cook, R. C, 273. 
Coppenrath, E., 466. 
Cox, H. R., 221. 
Cowles, A. H., 380. 
Crosby, W. A., 36. 
Crowther, C, 429, 469. 
Cullen, J. A., 464. 
Cummins, A. B., 267. 
Curry, B. E., 267, 380. 
Curtis, R. E., 389. 
Cushman, A. S., 73, 132. 
Czermak, W., 143, 296. 

Damon, S. C, 381, 476, 560. 

Darbishire, F. V., 414. 

Davidson, G., 109. 

Davidson, J. B., 144. 

Davis, A. R., 432. 

Davis, N. B., 137. 

Davis, R. O. E., 171, 204. 

Davis, W. M., 46. 

Davy, J. B., 340. 

Demolon, A., 267, 467. 

Digby, Kenelm, 442. 

Diller, J. S., 33. 

Dobeneck, A. P., 156. 

Dorrance, R. L., 430. 

Dorsey, C. W., 330, 334, 337, 340. 

Doryland, C. J. T., 249. 

Duchacek, F., 460. 

Dugaidin, M., 467. 

Duggar, B. M., 432. 

Duley, F. L., 499. 

Dupre, H. A., 169. 

Dyer, Bernard, 318. 

Eastman, E. E., 204. 
Ehrenberg, P., 134, 143. 
Ellett, W. B., 362. 
Elliott, C. G., 210, 213. 
Emerson, H. L., 17, 40, 46. 
Ernest, A., 110, 252. 



Failyer, G. H., 77, 268, 279, 321. 

Faiire, L., 210. 

Feilitzen, H. von, 429, 467. 

Fellers, C. R., 387. 

Fippin, E. O., 122, 143, 211, 499, 516, 

.'519. 
Fisher, M. L., 204. 
Fleischer, M., 44. 
Fletcher, C. C, 71. 
Floess, R., 134. 
Floyd, B. F., 363. 
Flugel, M., 478. 

Fraps, G. S., 208, 319, 420, 443, 471. 
Frear, W., 362, 376, 377, 516, 524. 
Freckmann, W., 186. 
Fred, E. B., 505, 543. 
Fry, W. H., 6, 76, 133, 445, 455. 
Fulmer, H. L., 505. 
Funchess, M. J., 347. 

Gaither, E. W., 58, 499. 

Gainey, P. L., 249, 356, 392, 420, 424. 

Gallagher, F. E., 141, 143, 273. 

Gans. R., 265. 

Gedroiz, K. K., 459. 

Gee, E. C, 211. 

Georgeson, C. C, 239. 

Gerlach, U., 272, 306. 

Gilbert, J. H., 180, 443. 

Gile, P. L., 299, 376, 466. 

Gillespie, L. J., 281, 350, 356. 

Glass, J. S., 204. 

Goessman, C. A., 504. 

Gortner, R. A., 116. 

Grandeau, L., 115. 

Greaves, J. E., 392, 393, 420, 421, 422, 

432, 433. 
Gustafson, A. F., 124, 220, 242. 
Guthrie, F. B., 336. 

Haberlandt, H., 140, 224. 

Hall, A. D., 10, 68, 78, 206, 217, 284, 

287, 294, 305, 421, 433, 442, 

448, 449, 471, 508, 516, 519, 

531, 532. 
Halligan, J. E., 442, 471. 
Harned, H. H., 544. 
Harris, F. S., 328, 334, 336, 340. 
Hart, E. B., 303, 315, 468, 499, 514, 

521. 
Hart, R. A., 211, 340. 
Barter, L. L., 337. 



INDEX OP AUTHORS 



563 



Hartwell, B. L., 347, 349, 354, 381, 461, 

476, 560. 
Hasenbaumer, J., 466. 
Headden, W. P., 330, 332. 
Heinrich, R., 197. 
Hellriegel, H., 189, 191, 192. 
Helms, R., 336. 
Hendrick, J., 78. 
Hibbard, P. L., 342. 
Hildebrandt, F. M., 267. 
Hilgard, E. W., 31, 68, 73, 116, 120, 

155, 162, 330, 340. 
Hill, H. H., 550. 
Hills, J. L., 483. 
Hiltner, L., 389. 
Hirst, C. T., 464. 
Hitchcock, E. B., 421. 
Hoagland, D. R., 279, 280, 281, 284, 

285, 323, 350. 
Hoffman, C, 461. 
Hopkins, C. G., 122, 355, 362, 437, 466, 

516, 533, 539, 540, 545. 
Houston, H. A., 116. 
Howard, L. P., 353, 354. 
Hubbard, P., 73. 
Hudelson, R. R., 362. 
Hudig, J., 429. 
Humphreys, W. J., 53. 
Hunt, T. F., 472, 533. 
Hurst, L. A., 350, 356. 
Hutchinson, C. M., 545. 
Hutchinson, H. B., 108, 355, 387, 402, 

411, 414, 415, 424, 447, 450, 

544. 

Ingle, Herbert, 100. 
Isham, R. M., 332. 
Israelsen, O. W., 92, 93, 163. 

Jaffrey, J. A., 211. 
Jensen, C. A., 545. 
Jodidi, S. L., 106, 248. 
Joffe, J. S., 351, 356. 
Johnson, H. W., 405. 
Johnson, S. W., 249. 
Jones, C. H., 355, 483. 
Jones, S. C, 499. 
Juritz, C. F., 430. 

Karraker, P. E., 163, 171, 358. 
Kaserer, H., 416. 



Kearney, T. H., 337. 

Keen, B. A., 151. 

Kellerman, K. F., 424. 

Kellner, O., 450. 

Kellogg, E. H., 405. 

Kellogg, J. W., 365, 379. 

Kelley, N. P., 107, 267, 347, 415, 421. 

450. 
Kelly, M. P., 466. 
Kiesselbach, T. A., 188. 
King, F. H., 94, 145, 163, 172, 176, 

189, 210, 230, 241, 242, 282, 

284, 422. 
Kinnison, C. S., 140. 
Klippart, J. H., 210. 
Knox, J., 450. 
Knox, W. H., 355. 
Knudson, L., 402. 
Koch, G. P., 388. 
Konig, J., 466. 
Kopecky, J., 179. 
Kopeloff, N., 377, 387, 388, 413. 
Koppers Company, The, 449. 
Kratzman, E., 347. 
Krusekopf, H. H., 362. 
Krzymowski, R., 187. 



Lang, C, 228, 232. 

Lapham, M. H., 171. 

Lathrop, E. C, 107, 410. 

Latshaw, W. L., 437. 

Lau, E., 248. 

Lawes, J. B., 180, 189, 443. 

Leather, J. W., 190. 

Leidigh, A. H., 211. 

Lemmermann, O., 551. 

Liebig, J. Justus von, 443. 

Lipman, C. B., 32, 158, 278, 376. 

Lipman, J. G., 307, 342, 381, 384, 403, 

406, 431, 433, 436, 508, 537, 

556, 560. 
Loew, 0., 376, 415. 
Lohnis, F., 433. 
Loughridge, R. H., 78, 122, 156, 198, 

337. 
Lugner, I., 429. 
Lyon, T. L., 179, 181, 207, 251, 252, 

284, 297, 422, 436, 437, 495, 

541, 542. 
Lynde, C. J., 169. 
Lynde, H. M., 211. 



564 



INDEX OF AUTHORS 



Maclntire, W. H., 181, 250, 345, 370, 

371, 422. 
MacLennan, K., 355. 
Martin, J. C, 280, 285. 
Martin, L. M., 46. 
Martin, T. L., 541, 545, 547. 
Martin, W. H., 351. 
Marchal, E., 335, 413. 
Marshall, C. E., 384. 
Massey, A. B., 109. 
May, D. W., 466. 
Mayer, A., 200. 
Maynard, L. A., 545. 
Maze, P., 402, 478. 
McBeth, I. G., 267, 389. 
McBride, F. W., 116. 
McCall, A. G., 267, 278. 
McCaughey, W. G., 6, 36, 76, 
McCool, M. M., 362. 
McDole, G. R., 118, 166. 
McGeorge, W. T., 78, 79, 273. 
McLane, J. W., 168, 277. 
McLean, H. C, 388. 
McMlllar, P. R., 380. 
Merrill, G. P., 3, 17, 32, 36, 38, 265. 
Middleton, H. E., 133. 
Miles, M., 210. 
Millar, C. E., 362. 
Miller, B. L., 448. 
Miller, E. C, 190, 194. 
Miller, M. F., 362. 
Miller, N. H. J., 10, 108, 402, 411, 415, 

447, 450, 469. 
Milligan, S., 545. 
Miner, H. L., 483. 
Minges, G. A., 421. 
Mirasol, J. J., 347, 349. 
Mitscherlich, E. A., 134, 140, 186, 284, 

477. 
Miyake, K., 347. 
Molisch, H., 296. 
Montgomery, E. G., 188, 190, 191, 

192. 
Mooers, C. A., 181, 362. 
Moore, C. J., 133. 
Morgan, J. F., 278, 281, 282. 
Morrow, C. A., 99, 105. 
Morse, F. W., 122, 267, 380, 449. 
Morse, W. J., 465. 

Mosier, J. G., 124, 204, 219, 220, 242. 
Murray, T. J., 427, 509. 
Mulder, T. J., 105. 



Neller, J. R., 256, 465. 
Niklas, H., 127. 
Norton, T. H., 450. 

Ogg, W. J., 78. 
Oliver Plow Book, 144. 
Olsen, C, 351. 
Osborne, T. B., 68, 70. 
Osugi, S., 346, 349. 
Owen, W. L., 256. 

Pantanelli, E., 284. 

Parker, E. G., 267, 269, 271. 

Parker, F. W., 278. 

Parks, J., 242. 

Parsons, L. J., 210. 

Patten, H. E., 154, 232, 235, 237, 263, 

273. 
Patterson, J. W., 420. 
Peake, W. A., 113. 
Peck, E. L., 469. 

Pember, F. R., 347, 349, 354, 381, 461. 
Penny, C. L., 537, 540. 
Peters, E., 266, 271. 
Peterson, W. H., 303, 315, 331, 332, 

468. 
Pettit, J. H., 355. 
Pfeiffer, Th., 478. 
Pick, H., 134. 
Pickel, G. M., 44. 
Pieters, A. J., 537. 
Piper, C. v., 537. 
Pirsson, L. V., 3, 46. 
Pitman, D. W., 336. 
Pitra, J., 460. 
Plummer, J. K., 5, 6, 76, 251, 256, 356, 

373, 392, 420. 
Potter, R. S., 251, 315. 
Pranke, E. J., 451. 
Prescott, J. A., 263. 
Prianischnikov, D., 459, 460. 
Prince, A. L., 354, 356. 
Puchner, H., 78, 141. 
Pugh, E., 443. 

Rahn, Otto, 392. 
Ramann, E., 127, 259. 
Ramser, C. E., 204. 
Ramsower, H. C, 145. 
Rather, J. B., 113. 
Ravin, P., 402. 
Reed, H. S., 109, 297. 



INDEX OF AUTHORS 



565 



Reid, V. R., 347, 466. 

Reimer, F. C, 407. 

Rice, F. E., 346, 349. 

Richards, E. H., 429. 

Richmond, T. E., 406. 

Roberts, I. P., 504, 514, 519, 521. 

Robbins, W. J., 109. 

Robbins, W. W., 386. 

Robinson, C. S., 44. 

Robinson, F. W., 539. 

Robinson, G. W., 78. 

Robinson, W. O., 5, 13, 14, 86, 41, 52, 

63, 77, 118, 466. 
Rodewald, H., 134. 
Ross, W. H., 464, 466. 
Rost, C. O., 63, 118, 119, 315. 
Ruprecht, R. W., 347, 449. 
Russell, E. J., 9, 68, 78, 158, 248, 252, 

253, 257, 273, 387, 414, 424, 

429, 471, 543. 
Russell, I. C, 46. 
Ruston, A. G., 429, 469. 

Sachs, J., 296. 

Sachs, W. H., 466. 

Sackett, W. G., 331, 412. 

Salisbury, R. D., 52, 57. 

Salter, R. M., 116. 

Saussure, Theodore de, 442. 

Schantz, H. L., 156, 188, 190, 195, 196, 

197. 
Schoilenberger, C. J., 315, 354. 
Schone, E., 73. 
Sehreiner, 0., 105, 107, 108, 109, 111, 

268, 279, 297, 321. 
Schulze, F., 322. 
Schutt, M. A., 507, 519. 
Seelhorst, C, von, 186, 187, 192. 
Sewell, M. C, 144, 220, 221. 
Sharp, L. T., 281, 350. 
Shaw, C. F., 92. 
Shedd, 0. M., 325, 406, 467. 
Sherman, J. M., 387. 
Shorey, F. C, 76, 105, 107, 362. 
Shutt, F. T., 430, 539. 
Singewald, J. N., 448. 
Skinner, J. J., 108, 109, 347, 351, 447, 

466. 
Slosson, E. E., 450. 
Smalley, H. R., 44, 347. 
Smith, Alfred, 89. 
Smith, C. D., 539. 



Smith, O. C, 116. 

Snyder, H., 122, 284, 317, 545. 

Snyder, R. S., 251, 313, 315. 

Spillman, W. J., 537. 

Spurway, C. H., 287. 

Stephenson, R. E., 353, 354. 

Stevenson, W. H., 44. 

Stewart, C. F., 45. 

Stewart, G. R., 279, 280, 284, 323. 

Stewart, R., 331, 332, 376, 381, 404, 

420, 422, 470. 
Stoddard, C. W., 100. 
Stoklasa, J., 110, 252, 255, 256, 460. 
Storer, F. H., 504, 537. 
StiJnner, K., 3,v9. 
Stremme, H., 134. 
Strowd, W. H., 435. 
Sullivan, E. C, 267, 270. 
Sullivan, M. X., 107, 466. 
Swanson, C. O., 437. 
Sweetser, W. S., 511. 
Swezey, G. D., 242, 260. 
Tacke, Br., 355. 
Tartar, H. V., 467. 
Tarr, R. S., 46. 
Taylor, W. W., 127. 
Tempany, H. A., 134. 
Temple, J. C, 421. 
Thatcher, R. W., 100, 122, 127. 
Thomas, W., 376, 377. 
Thompson, H. C, 44. 
Thorne, C. E., 375, 382, 454, 461, 462, 

499, 504, 507, 511, 513, 514, 

516, 519, 521, 525, 526, 528, 

529, 532, 533. 
Tottingham, W. E., 461, 514. 
Triesehmann, J. E., 469. 
Tmka, R., 92. 
True, R. H., 300, 346, 348. 
Truog, E., 348, 359. 
Turpin, H. W., 252. 

Ulrich, R., 232, 233. 
Underwood, T. M., 284, 287. 

Vageler, P., 134. 

Van Bemmelen, J. M., 36, 106, 132, 265, 

266, 270. 
Van Slyke, L. L., 442, 471, 501, 503, 

514. 
Van Suchtelen, F. H. H., 278. 
Veitch, F. P., 317, 355. 



566 



INDEX OF AUTHORS 



Voelcker, A., 519, 532. 
Von Englen, O. D., 58. 
Voorhees, E. B., 431, 504. 
Vrooman, C, 439. 

Waggaman, W. H., 263, 455, 456, 461, 

464. 
Wagner, F., 239. 
Wagner, H., 477. 
Waksman, S. A., 387, 388, 389, 392, 

413. 
Walker, S. S., 51, 118. 
Walters, E. H., 107. 
Warington, R., 113, 132, 144, 180, 182, 

265, 303, 426. 
Warner, H. W., 406. 
Warren, G. M., 210. 
Watson, G. C, 514. 
Way, J. T., 132, 264. 
Waynick, D. D., 113. 
Weaver, F. P., 499. 
Weir, W. W., 362. 
Welitschkowsky, D., von, 176. 
Wells, A. A., 248. 
Wills, C. F., 116. 
Westerman, F., 433. 
Whitbeck, R. H., 58. 
Whitney, M., 81, 83, 85, 89. 
Whisenand, J. W., 520. 



White, J. W., 351, 353, 365, 377, 421, 

449, 550. 
Whiting, A. L., 545. 
Whitson, A. R., 44, 204, 362, 422. 
Wiancko, A. T., 365, 381, 461, 499. 
Widtsoe, J. A., 172, 186, 187, 190, 192. 
Wiegner, G., 127, 265, 270. 
Wiley, H. W., 73, 112, 114, 115, 314. 
Williams, C. B., 49, 52, 118. 
Williams, H. F., 5. 

Wilson, B. D., 11, 374, 404, 430, 437. 
Wilson, G. W., 388. 
Wilson, J. K., 297. 
Wing, H. H., 514. 
Winogradsky, S., 431. 
Wolkoff, M. I., 131. 
Wollny, E., 110, 163, 171, 176, 189, 

200, 228, 230, 245. 
Wood, T. B., 516. 
Woodward, S. M., 210. 
Wright, R. C, 541. 
Wyatt, F. A., 363, 376, 381. 
Wyckoff, M. I., 267. 

Yarnell, D. L., 211. 
Yoder, P. A., 73. 
Young, G. J., 464. 
Young, H. J., 221. 

Zzigmondy, R., 127. 



INDEX OP SUBJECT MATTER 



Ability of plants to grow on poor soils, 

299. 
Abrasion defined, 18. 
Absorption by litter, 521. 
Absorption, by soils explained, 263. 

capacity of soils to retain nitrates, 
321. 

due to soil colloids, 26.'j. 

effect of on soil acidity, 352. 

efl^^ect of texture on, 267. 

importance of in soils, 273. 

of litter in stable, 521. 

selective by soils, nature of, 269. 

selective by soils, types of, 269. 
Absorption by soils, capacity for, 266. 

causes of, 264. 

defined, 263. 

importance of, 273. 

influence of time on, 269. 

law of, 269. 

relation to acidity, 274. 

relation to the soil solution, 276. 

selective, 269. 

types of, 263. 
Absorption of solar insolation, as influ- 
enced by atmosphere, 226. 

as influenced by color, 228. 

as influenced by slope, 229. 

as influenced by soil, 226. 
Absorptive capacity of different crops, 

301. 
Acid phosphate, 456. 

changes in soil, 457. 

character, 456. 

compared with rock phosphate, 458. 

composition, 456. 

manufacture, 456. 

reinforcement of manure with, 528. 
Acidity, as influenced by absorption, 274. 

development of by hydrolysis, 348. 

production of by selective absorp- 
tion, 270. 

soil, nature of, 345. 
Acids, production of by plant roots, 296. 
Actinomyces in soils, character of, 389. 



Actinomyces in soils, importance of, 389. 

number of, 289. 
Addition of nutrients to soil, 556. 
Additions to and losses from soil under 

various types of farming, 558. 
Adobe, inportance of, 64. 

origin of, 64. 

wind formation of, 21. 
iEolian soils, adobe, 64. 

loess, 61. 

sand dunes, 64. 

volcanic dust, 65. 
ASration of soil, effect on nitrification, 
418. 

importance in soil, 256. 

influence on bacteria in soils, 393. 
Agglutination of colloids, 131. 
Agricultural lime, defined, 363. 

forms of, 363. 
Agricultural value of farm manure, 513. 
Air of the soil, carbon dioxide of, 250. 

composition of, 247, 248. 

composition data, 248, 250. 

effect of oxidation on, 254. 

general characteristics of, 247. 

importance of oxygen in, 256. 

practical modification of, 261. 

movement of, 258. 

types of, 249. 

volume of, 257. 
Alkali, black, 329. 

composition of, 329. 

conditions affecting influence of, 338. 

control of, 343. 

control of by means of gj-psum, 342. 

effect of concentration of on crops, 
337. 

effect on crops, 334. 

effect on soil organisms, 335. 

eradication of, 341. 

eradication of by means of drainage, 
341. 

influence on nitrification, 421. 

in river water, 332. 

in irrigation water, 334. 



567 



568 



INDEX OF SUBJECT MATTER 



Alkali, origin of, 331. 

resistance of crops to, data on, 338. 

rise of as influenced by irrigation, 
339. 

white, 329. 
Alkali lands, handling of, 340. 
Alkali salts, listed, 330. 
Alkali soils, defined, 328. 

importance of, 328. 
Alkali spots, nature of, 332. 
Alkali tolerance by plants, factors of, 

336. 
Alkali vegetation, 340. 
Alluvial fans, 47. 
Alluvial soils, chemical composition, 49. 

classified, 46. 

deltas, 47. 

fans, 47. 

flood plain, 47. 

importance of, 49. 

origin of, 46. 
Aluminum, hydrolysis of in soil, 348. 

relation of to soil acidity, 347. 

relation to the reversion of acid 
phosphate, 457. 
Alunite as a fertilizer, 465. 
Amino acids defined, 106. 

in farm manure, 510. 
Amides defined, 106. 
Ammonia in rain water, data on, 429. 
Ammonification, conditions for, 414. 

influence of protozoa on, 387. 

nature of, 412. 

organisms of, 413. 

products of, 413. 

reactions of, 414. 
Ammonifying efficiency of soil, determi- 
nation of, 414. 
Ammonium salts, utilization by higher 

plants, 415, 450. 
Ammonium sulfate, changes in soil, 449. 

character of, 449. 

composition of, 449. 

source of, 449. 
Amounts of fertilizer to apply, 492. 
Amounts of lime to apply, 368. 
Analysis of plant tissue, method of, 102. 
Analysis of soil, bulk, 311, 314. 
carbon in, 113, 114. 
extraction, dilute acids, 317. 
extraction, strong acids, 316. 
extraction, with water, 319. 



Analysis of soil, humus, 115. 

lime requirement of, 355. 

minerological, 76. 

nitrogen in, 311. 

organic matter of, 115. 

value of, 323, 326. 
Apatite in soil, 6. 

Application of farm manure, amounts, 
526. 

evenness, 526. 

incorporation in soil, 526. 
Arid soils, biological activity in, 32. 

chemical analysis of, 31. 

humus content of, 120. 
Assimilation of nitrates by soil organ- 
isms, 426. 

importance of, 428. 
Available water in soil, 198. 
Availability of nitrogen fertilizers, 454. 

of phosphate fertilizers, 458. 
Azofication, amount of nitrogen fixed, 
433. 

energy for, 432. 

organisms of, 432. 
Azotohacter ehroococcum in soil, 431. 

B. Radicicola, amount of nitrogen fixed 
by, 437. 

availability of nitrogen fixed by, 437. 

function of, 434. 

importance of, 436. 

inoculation of the soil, methods of, 
439. 

nature of organism, 435. 

nodules of, 434. 

relation to host plant, 435. 

strains of, 434. 
Bacteria, decomposition of organic mat- 
ter by, 103. 

increase of in frozen soil, 394. 

influence on aeration in soils, 393. 

injurious to higher plants, 396. 

method of counting in soil, 392. 

multiplication of, 391. 

production of carbon dioxide by, 252. 

relation of to alkali, 332. 

relation to liming, 395. 

relation of moisture to, 393. 

relation to organic matter in soil, 
394. 

relation to soil acidity, 395. 

relation to soil temperature, 394. 



INDEX OF SUBJECT MATTER 



569 



Bacteria, shape of, 391. 

seasonal flora, 394. 

spore formation by, 391. 
Bacteria in soils, character of, 390. 

determination of numbers of, 392. 

factors affecting growtli of, 393. 

influence of green manures on, 544. 

numbers of, 392. 

position in soil, 391. 

production of enzjones by, 390. 

size of, 391. 
Bacterial activity, measured by carbon 

dioxide produced, 25C. 
Bacterial growth, conditions affecting, 

393. 
Bases, substitution of in soils, 271. 

those used to correct soil acidity, 
362. 

toxic nature of in acid soils, 346. 
Basic exchange, 270. 

influence on drainage water, 305. 
Basic slag, changes in soil, 458. 

character of, 458. 

composition of, 457. 

source of, 457. 
Beaker method of mechanical soil analy- 
sis, 69. 
Biological cycles of the soil, importance 
of, 398. 

names of, 399. 

nature of, 398. 
Biological effects of lime on soil, 371. 
Bog lime, nature of, 45. 
Bomb method for determining soil or- 
ganic matter, 114. 
Bone phosphate, changes in soil, 455. 

character, 454. 

composition, 454. 

source, 454. 
Brands of fertilizers, 478. 
Bromberg soil tank.s, data from, 306. 
Brownian movement, explained, 128. 
Bucher method of fixing nitrogen, 453. 
Bulk analysis of soils, carbon and nitro- 
gen, 311. 

mineral constituents, 314. 
Burned lime, 364. 

Calcium, amount in soils, 13. 
forms of in soil, 11. 
importance of in fertility evalua- 
tions, 324. 



Calcium, in soil minerals, 6. 

lack of in relation to soil acidity, 
348. 

loss of from soil, 307, 370, 555. 

of di-silicate as an amendment, 380. 

relation to reversion of acid phos- 
phate, 457. 

use of as lime, 363. 
Calcium eyananiid, change in soil, 452. 

character of, 452. 

composition of, 452. 

manufacture of, 451. 
Calcium and magnesium ratio in soils, 

375. 
Calcium in gypsum as an amendment, 

379. 
Calcium losses, Bromberg lysimeters, 30G. 

from Cornell soils, 307. 
Calcium nitrate, character of, 452. 

composition of, 452. 

manufacture of, 452. 
Capillary-absorbed water, defined, 196. 
Capillary capacity of soils, factors affect- 
ing, 163. 
Capillary film, thickness of and effect on 

capillary movement, 171. 
Capillary movement of soil water, data 
on rate, 174. 

effect of structure on, 174. 

effect of texture on, 173. 

factors affecting, 170. 

explained, 168. 

influence of film thickness, 171. 

relation to soil mulch, 175. 

role in supplying plants with water, 
193. 
Capillary pull of soils, data on, 169. 

determination of, 168. 
Capillary water of soil, amounts in soil 
columns, 165. 

colloidal control of, 159. 

defined, 159. 

determination of amount, 161. 

kinds of, 159. 

position of inter film, 160. 

surface tension control, 159. 
Carbide method of fixing nitrogen, 451. 
Carbon, cycle of in soil, 399. 

determination of in soil, 113. 

gain of by green manures, 539. 

in Cornell drainage water, 402. 

in organic matter, 113. 



570 



INDEX OF SUBJECT MATTER 



Carbon, loss from the soil, data of, 402. 
loss of from soil, 555. 
use of organic carbon by higher 
plants, 402. 
Carbon cycle of the soil, loss of carbon 
from, 400. 
nature of, 399. 
organisms of, 399. 
products of, 400. 
Carbon dioxide, a measure of bacterial 
activity, 256. 
from decaying manure, 509. 
from lime, 369. 
function in soil, 255. 
in atmospheric air, data, 110. 
in soil air, data, 110. 
influence on nitrification, 256, 419. 
relation to mineral cycle of soil, 408. 
of soil air, 250. 
of soil air, influence of farm manure 

on, 254. 
of soil air, influence of organic mat- 
ter on, 253. 
production of, 110. 
produced by bacteria in soil, 252. 
produced by plant roots, 252, 295. 
source of in soil air, 251, 400. 
Carbonated lime, 3G5. 
Carbonation, influence in soil formation, 

26. 
Carbonized materials in soil, importance 
of, 112. 
nature of. 111. 
Castor pomace, composition of, 446. 
Catalytic fertilizers, 466. 
Catalyst defined, 103, 135. 
Cell sap, nature of in relation to plant 

absorption, 300. 
Centrifugal mechanical analysis of soils, 

71. 
Character of soil particles, 69. 
Chemical absorption by soils, 263. 
Chemical analysis, alluvial and upland 
soils, 49. 
arid and humid soils, 31. 
bulk and extraction methods, 311. 
by digestion with strong acids, 316. 
by wateT extraction, 319. 
glacial soils, 57. 
granite soil, 33. 

importance in fertility evaluation, 
323. 



Chemical analysis, limestone soil, 33. 

loess soils, 63. 

marine soils, 52. 

of alkaline river water, 334. 

of Cornell soils, 325. 

of good and poor Ohio soils, 326. 

of Minnesota soils, 316. 

of Minnesota and Maryland soils, 

317. 
of soil, popular conception of, 311. 
of soil separates, 78, 79. 
peat and muck, 44. 
residual soils, 41, 52, 57. 
resume as to value of, 326. 
value as shown by actual data, 326. 
with weak acids, 317. 
Chemical composition of soils, compared 

to lithosphere, 13. 
Chemical composition of soil separates, 

78, 79. 
Chemical effects of lime on soil, 371. 
Chromic acid method for determination 

of soil organic matter, 113. 
Chile salt petre, source and character of, 

448. 
Classification of methods of mechanical 

analysis, 72. 
Classification of soils, geological, 38. 

for soil survey, 85. 
Classification of soil particles, Bureau of 

Soils, 67. 
Classification of soil particles other than 

Bureau of Soils, 68. 
Climate, effect on transpiration, 191. 
relation of to soil formation, 30. 
Clostridium pastorianutn in soil, 431. 
Coastal plain soils, chemical composition 

of, 52. 
Cohesion, cause of in soils, 136. 

defined, 136. 
Colloidal materials, properties of, 130. 

in soils, 265. 
Colloidal matter, absorptive power for 

water, 153. 
Colloidal matter, influence on soil prop- 
erties, 135. 
Colloidal matter in soils, influence on 
structure, 137. 
estimation of, 134. 
generation of, 132. 
resume of, 138. 
Colloidal particles, size of, 128. 



INDEX OF SUBJECT MATTER 



571 



Colloidal state, defined, 127. 

defined briefly, 75. 

electrical condition of, 131. 

examples of, 130. 

phases of, 129. 

practical importance of, 135. 

relation of to granulation, 142. 
Colloids and crystalloids, 129. 
Color of soil, compounds of, 36, 37. 

influence on absorption of insulation, 
228. 

nature of, 36. 
Colluvial soils, origin and nature, 45. 
Commercial fertilizer, amounts to apply, 
492. 

development of use, 442. 

used for their nitrogen, 444. 

used for their phosphorus, 454. 

used for their potash, 462. 

used in United States, 444. 
Commercial value of fami manure, 512. 
Composition of average soil, 12. 

of cow manure, 501. 

of drainage water, 304. 

of farm manure, average, 504. 

of horse manure, 501. 

of muck and peat, 44. 

of plant tissue, 100. 

of sheep manure, 501. 

of swine manure, 501. 
Composts, use of manure in, 530. 
Composts of sulfur, 406. 
Conductivity of heat, measurement of, 
235. 

formula for, 236. 
Conductivity coefficients of various soils, 

236. 
Conductivity of various soils, 235. 
Conduction, loss of heat from soil by, 

240. 
Conduction of heat in soils, factors af- 
fecting, 235. 

nature of, 234. 
Constituents of soil, organic and inor- 
ganic, 2. 
Control of alkali in soils, 343. 

of evaporation, 218. 

of soil air, 261. 

of soil temperature, 244. 
Conservation of soil moisture, 219. 
Conversion factors for lime, 367. 
Convection of heat in soil, 238. 



Correction of soil acidity, bases useful 

for, 363. 
Corrosion defined, 18. 
Cotton and tobacco, influence of manure 

on, 535. 
Cotton seed meal, composition of, 446. 
Cover crops, influence on nitrates of soil, 

541. 
Crop resistance to alkali, generalized 
table of, 338. 
in pounds per acre, 338. 
Crop residues, to maintain organic mat- 
ter, 124. 
Crop rotation, relation of to green ma- 
nuring, 552. 
Crops, absorptive capacity of, 301. 
amounts of fertilizers for, 493. 
bacteria injurious to, 390. 
detrimental influence of nitrogen on, 

473. 
effect of calcium and magnesium 

ratio on, 376. 
effect of concentration of salts on, 

337. 
effect of on conservation of plant 

nutriants, 308. 
fertilizer formulae for, 491. 
for green manures, 546. 
fungi injurious to, 396. 
influence of green manures on, 547. 
influence of manure on, 532. 
influence of nitrogen on, 472. 
influence of phosphorus on, 474. 
influence of potassium on, 475. 
injurious effect of soil organisms on, 

396. 
quantities of nutrients removed by, 

303. 
removal of nutrients by, 555. 
removal of sulfur by, 404. 
removal of sulfur and prohphorus 

by, 468. 
response to lime, 372. 
systems of fertilizing, 496. 
Crushers, action of, 148. 
Cultivation, implements for, 147. 

importance of, 219. 
Cultivators, action of, 147. 
Cumulose soils, agricultural importance, 
43. 
location of, 42. 
origin, 42. 



572 



INDEX OF SUBJECT MATTER 



Decay and decomposition defined, 103, 
410. 
and putrefaction, in nitrogen cycle, 

410. 
and putrefaction, organisms of, 411. 
effect on soil temperature, 239. 
of farm manure, importance of, 511. 
of green manure, influence on lime 

and phosphorus, 545. 
of green manure, influence on nitrate 

accumulation, 543. 
of green manure, influence on nitri- 
fication, 544. 
of green manure, stages of, 542. 
of organic matter in soil, products 
of, 110. 
Decomposition, defined, 17. 

of organic matter in soil, 103. 
Delta soils, 47. 

Denitrification, use of term, 426. 
Deoxidation, influence in soil formation, 

24. 
Deposition, its relation to soil formation, 
16. 
relation to lime requirement, 356. 
Depression of the freezing point, a 
method of studying soil solu- 
tions, 280. 
Determination of soil humus, 115. 
Determination of soil organic matter, 
bomb method, 114. 
chromic acid method, 113. 
loss on ignition, 112. 
Di-calcium silicate as a soil amendment, 

380. 
Diffusion, differential into plants, 292. 
of nutrients into plants, 291. 
of soil air, 260. 
Diminishing returns, law of, 493. 
Disc plow, influence on soil, 146. 
Disintegration, defined, 17. 
Dissociation, defined, 270. 
Drainage and evaporation at Rotham- 

sted, 217. 
Drainage, importance of, 210. 
influence of, 210. 
loss of sulfur by, 404. 
nutrient losses from .soil, 555. 
qualitative composition of water of, 

304. 
quantitative composition of water 
of, 304. 



Drainage, use of in eradication of alkali, 
341. 

usual type of, 212. 
Drainage water, carbon in, 402. 

composition data of, 305. 

composition of, at Bromberg, 272. 

importance of study, 178. 

qualitative composition of, 304. 

quantitative composition of, 304. 
Dried blood, changes in soil, 445. 

character, 445. 

composition, 445. 

source, 445. 
Earth worms, importance of, 385. 
Earth's crust, minerals in, 4. 
Electric arc method of fixing nitrogen, 

452. 
Electrolyte, defined, 130. 

effect on colloids, 131. 
Element in the minimum, 476. 
Energy necessary for evaporation of 

water, 241. 
Energy, wave length of, 225. 
Enzymes, action of, 390. 

defined, 103, 390. 

importance in soils, 103. 
Eradication of alkali from soils, 341. 

types of, 341. 
Erosion defined, 18. 

relation to soil movement, 16. 
Erosion of soil, control of, 204. 

types of, 205. 
Evaluation of farm manure, 512. 
Evaporation and drainage at Rotham- 

sted, 217. 
Evaporation of soil moisture, control of, 
218. 

energy necessary for, 241. 

influence of on soil heat, 241. 

loss of soil water by, 216. 

water influenced by, 182. 
Exfoliation in soil formation, 21. 
Exhaustion of soil, discussion of, 309. 

possibility of, 308. 
Exosmosis, nature of, 290. 
Extraction of soils, with concentrated 
acids, 316. 

with dilute acids, 317. 

with water, 319. 

with water, successive extractions, 322. 
Exudates, excretion of by plant roots, 
296. 



INDEX OF SUBJECT MATTER 



573 



Factors influencing rise of soil tempera- 
ture, 231. 
Fami manure, a direct and indirect fer- 
tilizer, 504. 
agricultural value of, 513. 
agn"icultural value of protected ma- 
nure, 525. 
amounts applied, 527. 
amount produced by cows, 514. 
amounts produced by farm animals, 

513. 
amount produced by horses, 514. 
amount produced by poultry, 514. 
amount produced by sheep, 514. 
amount produced by steers, 514. 
amount produced by swine, 514. 
average composition of, 504. 
care of in stalls, 520. 
characteristics of, 500. 
commercial evaluation of, 512. 
composition of from various animals, 

501. 
covered yards for, 523. 
effect on carbon dioxide of soil air, 

254. 
eflicient application of, 525. 
evaluation of, 512. 
factors influencing composition of, 

506. 
fermentation and putrefaction of, 

508. 
fresh and well rotted compared, 511. 
fresh and yard, crop effects, 512. 
hauling directly to field, 521. 
importance of, 499. 
importance of its decay, 511. 
importance of protection, 524. 
importance of tight floors, 521. 
influence of handling on, 507. 
influence of tramping on, 524. 
influence on cotton, 535. 
influence on maize, 534. 
influence on meadows, 532. 
influence on potatoes, 534. 
influence on tobacco, 535. 
liquid and solid compared, 502. 
loss of constituents from, 508, 515. 
losses during handling and storage, 

519. 
maintenance of .soil organic matter 

by, 124, 519, 559. 
modern manurial practice, 520. 



Farm manure, nutrient lo.sses during pro- 
duction, 51C. 
outstanding characteristics of, 505. 
piles outside, 522. 
pits for, 523. 
place in rotation, 532. 
produced by animals, calculation of, 

514. 
products of decay, 510. 
reinforcement of, 527. 
residual effects of, 531. 
resume of use, 535. 
use of in sulfur composts, 406. 
use of lime with, 530. 
use of litter with, 521. 
use in composting, 530. 
variability of, 506. 
Feldspar as a fertilizer, 465. 
Fermentation, defined, 103, 410. 

of farm manure, 508. 
Fertility, maintenance of as influenced by 

different types of farming, 558. 
Fertility of soil, defined, 554. 

effect on transpiration ratio, 192. 
possible exhaustion of, 308. 
Fertility evaluations by means of a 

chemical analysis, 323. 
Fertilization, systems of, 496. 
Fertilizers, advantages of liome mixing, 
485. 
amounts to apply, 492. 
brands of, 47s. 

calculations of for lionie-mixing, 487. 
carrying free sulfur, 467. 
catalytic, 466. 
containing nitrogen, 444. 
containing phosphorus, 454. 
containing potash, 463. 
development of their use. 442. 
early use of, 442. 
effect of on soil acidity, 353. 
element in the minimum, 476. 
factors which determine the choice 

of, 488. 
farm manure, 504. 
formulre, for different soils and crops, 

491. 
formulae, nature of, 489. 
fomiuhe, theorj- of, 490. 
function of, 444. 
guarantees of, 481. 
how to buy, 483. 



574 



INDEX OF SUBJECT MATTER 



Fertilizer, how to home mix, 487. 

importance of high grade, 483. 

importance of residues from, 295. 

inspection and control, 480. 

interpretation of guarantee, 481. 

laws of, 480. 

law of diminishing returns, 493. 

low grade and high grade, 479. 

method and time of application of, 
495. 

purchase of unmixed, 484. 

rational utilization of, 497. 

systems of applying, 496. 

use in United States, 444. 

which should not be mixed, 486. 
Fertilizer mixtures, those of value, 487. 
Fertilizer practice, principles of, 471. 

rational system, 497. 
Fertilizer residues, cause of, 294. 

nature of from different salts, 294. 
Fillers, use of in fertilizers, 488. 
Fineness of limestone, data as to impor- 
tance, 377. 

importance of in liming, 377. 

influence of on decomposition, 378. 
Fish scrap, composition of, 446. 
Fixation of nitrogen artificially, 450. 

Bucher method, 453. 

carbide method, 451. 

electric arc method, 452. 

Haber method, 453. 
Fixation of nitrogen by free-living soil 
organisms, 430. 

by nodule bacteria, 433. 
Floats, see rock phosphate, 455. 
Flocculation, cause of, 131. 

defined, 130. 

relation of to granulation, 144. 
Flood plain soils, 47. 
Floors, importance in care of manure, 

521. 
Flue dust, a source of potash, 465. 
Food for plants, defined, 8. 
Forms of water in soil, diagram of, 199. 
Forms of soil water, 151. 
Forms of lime to apply, 367. 
Formulae of fertilizers for different soils 
and crops, 491. 

examples of, 489. 

theory of, 490. 
Freezing and thawing, effect on soils, 
23. 



Frost, importance in soil formation, 23. 
Fungi and algoe, smaller forms in soil, 
388. 

fixation of nitrogen by, 432. 

injurious to higher plants, 396. 

in soil, number of, 388. 

large forms in soil, 386. 

Germination of seeds, temperature of, 

224. 
Geological classification of soils, 38. 

resume of, 65. 
Glacial lakes, origin of, 59. 

soils of, 58. 
Glacial soils, chemical composition of, 
57. 

compared with residual, 57, 58. 

fertility of, 57. 

general character, 54. 

importance of, 57. 

origin, 54. 
Glaciation, American ice sheet, 53. 

effect of, 54. 

influence on agriculture, 58. 

in North America, 54. 
Glaciers in soil formation, 18. 
Grading of ground limestone, 377. 
Grandeau method, nature of, 312. 
Granite, cliemical composition of, 33. 

weathering of, 33. 
Grass, influence on nitrate accumulation, 
427. 

influence on nitrification, 422. 
Granulation of soil, as influenced by 
lime, 143. 

beneficial effects, 141. 

defined, 139, 141. 

forces producing, 143. 

influence of plowing on, 146. 

influence of tillage on, 144. 

production of, 142. 
Gravity water, amount soil will hold, 
177. 

calculation of, 178. 

factors affecting movement, 175. 

importance of study, 178. 
Green manures, ancient use of, 537. 

as cover crops, 538, 541. 

constituents gained by use of, 539. 

crops for, 545. 

decay of in soil, 541. 

general influence of, 538. 



INDEX OF SUBJECT MATTER 



575 



Green manures, importance of, 537. 

influence of decay of, !H3. 

influence of decay on lime and phos- 
phorus, 545. 

influence of decay on nitrate accu- 
mulation, 544. 

influence on crops, 552. 

influence on nitrate reduction, 426. 

manner of turning under, 549. 

practical utilization of, 552. 

relation of to the rotation, 552. 

relation to humus formation, 543. 

relative value of different crops for, 
547. 

time for plowing under, 548. 

to maintain organic matter, 123. 

use of, 548. 

use of lime with, 550. 
Ground limestone, 365. 
Guano, nature of, 445. 
Guarantees on fertilizers, statement of, 

481. 
Gullying and its control, 206. 
Gypsum as a soil amendment, 379. 

effect of on soils, 379. 

reinforcement of manure with, 527 

use of in alkali control, 342. 

Haber method of fixing nitrogen, 453. 
Handling of manure, covered yards, 523. 

hauling directly to field, 521. 

influence on composition, 507. 

manure pits, 523. 

piles outside, 522. 

care of in stalls, 520. 
Hematite, as a soil color, 37. 

change of to limonite, 27. 

formation of in soil, 25. 

source of in soil, 7. 
Heat, conduction of, 240. 

conduction of in soil, 234. 

conductivity of various soils for, 235. 

convection transfer of, 238. 

cycle between soil and atmosphere, 
225. 

factors affecting conduction of, 235, 
236. 

evaporation loss by, 241. 

importance In soil formation, 21. 

loss of from soil, 240. 

movement in soil, 234. 

radiation of, 240. 



Heat of wetting of soils, amount of, 153. 
data of, 154. 
effect of texture on, 154. 
significance of, 153. 
High grade fertilizers, importance of, 

4f3. 
Higher plants, influence on nitrification, 

422. 
Home-mixing of fertilizers, calculation 
of, 487. 
advantages, 485. 
good mixtures for, 487. 
how performed, 486. 
Hoof meal, composition of, 446. 
Humid soil, biological activity in, 32. 
chemical analysis of, 31. 
humus content of, 120. 
Humidity, influence of on the hygro- 
scopic coeflicient, 158. 
Humus, amount in California soils, 120. 
amount in Nebraska loess, 120. 
defined, 115. 

determination of, 115, 312. 
formation of from green manures, 
543. 
Hydration, influence of in soil formation, 

26. 
Hydrogen-ion concentration, a measure 
of soil acidity, 356. 
method of expression, 350. 
relation to soil acidity, 346. 
Hydrolysis, explanation of, 348. 

production of by enzymes, 390. 
Hygroscopic capacity of soils, data on, 

156. 
Hygroscopic coeflicient, data as to spe- 
cific soils, 157. 
defined, 152. 
determination of, 154. 
factors affecting, 157. 
range of in soils, 158. 
Hygroscopic water of soils, specific char- 
acter of, 153. 

Ice, disintegration of rocks by, 23. 

glacial, in soil formation, 18. 
Ice action, glaciation, 53. 
Ice age, 53. 

Ignition method for determining soil or- 
ganic matter, 112. 
Influence of alkali, condition affecting, 
338. 



576 



INDEX OF SUBJECT MATTEB 



Inoculation of soil with B. Radicicola, 

methods of, 439. 
Insulation, absorbed by earth's atmos- 
phere, 226. 
absorbed by soil, 227. 
absorption of as influenced by color, 

228. 
absorption of as influenced by slope, 

229. 
received by soil, 225. 
Insoluble phosphoric acid, defined, 456. 
Inspection and control of fertilizers, 480. 
Ions, absorption of by soils, 270. 
differential diffusion of, 293. 
diffusion of into plants, 291. 
Ionization, defined, 270. 

of water, 270. 
Irrigation, relation to rise of alkali, 339. 
Irrigation water, alkali content of, 333. 
Iron, in soil minerals, 7. 

relation to the reversion of acid 

phosphate, 457. 
relation of to soil acidity, 347. 

Kainit, reinforcement of manure with, 

527. 
Kaolinite, importance in soils, 7. 

source of in soil, 6. 
Kelp, a source of potash, 465. 
Kjeldahl method for determination of 
nitrogen, 312. 

Lacustrine soils, character of, 60. 

glacial lake, 58. 

importance of, 60. 

location in U. S., 60. 

recent lake, 60. 
Lake salines, a source of potash, 465. 
Law of diminishing return, 493. 
Leaching, effect of on soil acidity, 352 

loss of lime thereby, 370. 

use of in alkali eradication, 341. 
Leather meal, composition of, 446. 
Legumes, inoculation of, 438. 
Leguminous crops, amounts of nitrogen 
fixed by, 438. 

cross inoculation of, 434. 

effect on soil nitrogen, 437. 

nitrogen fixation by, 433. 
Leucite as a fertilizer, 465. 
Lime, agricultural terminology of, 364. 

agricultural use of, 363. 



Lime, amounts to apply, 368. 

biological effects in soil, 371. 
burned, 364. 
~ carbonated, 365. 
cause of crop response to, 372. 
changes in soil, 369. 
chemical effects of on soil, 371. 
composition of as sold in Pennsylva- 
nia, 366. 
contact action of, 374. 
conversion factors of, 367. 
crop response to, 372. 
effect of caustic forms on manure, 

530. 
forms of, 363. 
forms to apply, 367. 
importance of in soil improvement, 

381. 
influence of green manures on, 545. 
influence on availability of nutrients, 

373. 
influence on decay of green manures, 

651. 
influence on granulation, 143. 
influence on nitrification, 373. 
influence on soil bacteria, 395. 
influence on sulfofication, 405. 
losses from Cornell soils, 307, 370. 
methods of applying, 374. 
need of determinations, 365. 
physical effects on soil, 371. 
problem showing form to buy, 368. 
proper utilization of, 382. 
relation of to fertilizer mixtures, 

486. 
relation to reversion of monocalcium 

phosphate in soil, 457. 
relation to the use of manure and 

fertilizers, 382. 
time to apply, 374. 
use of manure with, 530. 
use of with green manure, 551. 
water slaked, 364. 
Lime requirement determinations, on 

soils, 355. 
types of, 355. 
Lime requirement of soils, Veitch method, 

35G. 
Limestone, amounts to apply, 368. 
burning of, 364. 
changes in soil, 370. 
chemical composition of, 33. 



INDEX OF SUBJECT MATTER 



577 



Limestone, conversion factors, 3C7. 
fineness of average product, .S78. 
fineness of for agricultural use, 307. 
grading of as to fineness, 377. 
importance of fineness, 377. 
mechanical composition as sold in 

Pennsylvania, 379. 
ratio of calcium and magnesium, 37.5. 
Liming, amounts of lime to apply, 368. 
calcium and magnesium ratio of, 

375. 
cause of crop response to, 372. 
crop response to, 372. 
forms of lime to apply, 367. 
importance of in soil improvement, 

381. 
method and time of applying lime, 

374. 
reasons for, 362. 
Limonite, source of in soil, 7. 

production of from hematite, 27. 
weathering of, 33. 
Limonite group, as soil color, 37. 
Linseed meal, composition of, 446. 
Lithosphere, composition of compared to 

soils, 13. 
Litmus paper test, criticism of, 360. 
procedure, 358. 

use of potassium nitrate with, 358. 
Litter, absorptive power of, 521. 

influence on character of manure, 
521. 
Loam, defined, 82. 
Loess, a wind laid soil, 21. 
character of, 62. 
chemical composition of, 63. 
importance of, 63. 
location of, 62. 
minerals of, 62. 
origin of, 61. 
Loss of nutrients from soil, 554. 

types of, 289. 
Loss of soil heat, by conduction, 240. 
by evaporation, 240. 
by radiation, 240. 
Loss of soil water by run off, 203. 
Losses during the production and han- 
dling of manure, 515. 
Losses from and addition to soils under 

various types of farming, 558. 
Lysimeter experiments, at Bromberg, 272. 
306. 



Lysimeter experiments, at Cornell Uni- 
versity, 307. 
at Rotliamsted Experiment Farm, 
180, 217, 288. 
Lysimcters, nature of, 180. 

of Cornell University, 181. 
of Rothamsted Experiment Station, 
180. 

Macro-organisms of the soil, 384. 
Maintenance of soil fertility, 554. 

influence of different types of farm- 
ing on, 558. 
program of, 560. 
Maintenance of soil organic matter, 122. 
Maize, influence of farm manure on, 534. 
influence on nitrate accumulation, 

428. 
influence on nitrification, 422. 
Manganese, relation of to soil acidity, 347. 
Mangum terrace, 205. 
Manurial practices, phases of, 520. 
Marine soils, character of, 51. 

chemical composition of, 52. 
importance of, 51. 
origin of, 50. 
Marl, origin and nature of, 45. 
term defined, 45. 
use of, 45. 
Maximum retentive power of soil for 
water, 162. 
determination of, 162. 
Maximum water capacity of soils, data 

on, 166. 
Meadows, influence of manure on, 532. 
Mechanical analysis of soils, 67. 
beaker method, 69. 
Bureau of Soils method, 71. 
determination of soil class from, 84. 
value of, 79. 
Mechanical analyses of typical soils, 83. 

of various soils, 81. 
Methods of applying fertilizers, 495. 
Methods of studying drainage losses, 180. 
Micro-organisms of the soil, 386. 
Micron, magnitude of, 128. 
Millimicron, magnitude of, 128. 
Mineral constituents of soils, bulk analy- 
sis of, 314. 
extraction of with dilute acids, 317. 
extraction of with strong acids, 316. 
extraction of with water, 319. 



578 



INDEX OF SUBJECT MATTER 



Mineral cycles in soils, importance of, 
408. 

nature of, 407. 

organisms of, 408. 

types of, 407. 
Minerals in earth's crust, 4. 
Minerals of the soil, 77. 

importance of, 6. 

list of, 5. 

source of, 4. 

specific gravity of, 89. 
Minerological analysis of soils, 76. 
Minerological character of soils, 77. 

of soil particles, 75. 
Minimum, element in the, 476. 

law of Mitscherlich, 477. 
Modification of soil air, 261. 
Moisture of soil, conservation by mulch, 
221. 

conservation, weed control, 220. 

control, summary of, 221. 

data for sandy and clayey soils, 
179, 200. 

determination on soil, method of, 
161. 

effect on heat conductivity, 236. 

effect on movement of soil air, 258. 

effect on nitrification, 420. 

effect on specific heat of soils, 233. 

influence on nitrification, 420. 

influence on bacteria, 393. 
Moisture equivalent of soils, defined, 167. 

for various soils, 168. 

method of determination, 167. 
Molecules, absorption of by soil, 269. 
Moraines, agricultural value, 54. 

ground, 54. 

terminal, 54. 
Movement of soil air, factors affecting, 

258. 
Muck, agricultural value of, 43. 

capacity for water, 164. 

character of, 43. 

chemical analysis of, 44. 

term defined, 43. 
Mulch, artificial, 218. 

soil, use of, 218. 
Muscovite, change of to kaolinite, 26. 

present in soils, 5, 77. 

Nitrates in alkali spots, 332. 
Nitrates in rain water, data, 429. 



Nitrates in soils, accumulation, 419. 

accumulation as influenced by green 

manure, 544, 549. 
accumulation, influence of grass on, 

427. 
accumulation, influence of maize on, 

428. 
as a source of nitrogen for higher 

plants, 415. 
assimilation of by soil organisms, 

426, 428. 
influence of green manures on, 543. 
production of. 111. 
reduction of, 424. 
Nitrate reduction, cause of, 425. 
control of, 426. 

influence of green manures on, 426. 
influence of straw on, 425. 
nature of, 425. 
organisms of, 425. 
Nitrification in soil, as affected by soil 

conditions, 418. 
as influenced by carbon dioxide, 256. 
efTect of aeration on, 418. 
effect of alkali on, 421. 
effect of carbon dioxide on, 419. 
effect of farm manure on, 418. 
effect of moisture on, 420. 
effect of soil acidity on, 421. 
effect of temperature on, 420. 
efficiency of, 417. 

influence of higher plants on, 422. 
influence of lime on, 373. 
influence of previous crops on, 423. 
influence on carbon dioxide produc- 
tion, 255. 
nature of, 415. 
organisms of, 415. 
products of, 415. 
reactions, 415. 

relation to ammonification, 416. 
relation of to carbon cycle, 408. 
relation of to mineral cycle, 408. 
relation to soil fertility, 423. 
Nitrifying organisms, types of, 415. 
Nitrites, production of in soils. 111. 
Nitrobacter in soil, 415. 
Nitrogen, additions to soil, by free-fixing 

organisms, 430. 
additions to soil, in manure, 557. 
additions to soil, in rain water, 429. 
additions to soil, modes of, 429. 



INDEX OP SUBJECT MATTER 



579 



Nitrogen, additions to soil, nature of, 429. 
amount fixed by li. Radiricola, 437. 
amount in ammonium sulfate, 449. 
amount in calcium cyanamid, 452. 
amount in calcium nitrate, 452. 
amount in California soils, 120. 
amount in dried blood, 445. 
amount in Nebraska loess, 120. 
amount in sodium nitrate, 448. 
amount in soils, 12. 
amount in soils of United States, 118. 
amount in tankage, 445. 
artificial fi.xation of, 450. 
availability of in fertilizers, 454. 
contained in rocks, 10. 
determination of in soils, 312. 
fixation by B. Radicicola, 433. 
fixed in soil by azofication, 433. 
forms of in ■ soil, 10. 
from B. Radicicola, availability of, 

437. 
gain due to green manures, 539. 
gain due to natural causes, 429. 
importance in biological processes, 

409. 
importance of in fertility evaluation, 

323. 
importance of in soils, 409. 
in farm manure, 501. 
in liquid and solid manure, 503. 
in rain water, data on, 429. 
inert character of, 409. 
influence on plant growth, 471. 
losses from Bromberg lysimeters, 

306. 
losses from Cornell soils, 307. 
losses from decaying manure, 511. 
losses from farm manure, 519. 
losses from soil, 555. 
natural addition to soil, 557. 
of food recovered in farm manure, 

516. 
organic forms used by plants, 411. 
possible detrimental influences of, 

473. 
relation of to life, 409. 
removed by crops from Cornell soils, 

325. 
utilization of organic forms by 

plants, 447. 
Nitrogen cycle, addition of nitrosen to 

soil by free-fixing bacteria, 430. 



Nitrogen cycle, addition of nitrogen to 
soil in rain water, 429. 
ammonification, 412. 
assimilation of nitrates by soil or- 
ganisms, 426. 
complexity of, 409. 
decay and putrefaction, 410. 
fixation of nitrogen by Azolohacter, 

432. 
fixation of nitrogen by B. Radici- 
cola, 433. 
nitrification, 415. 
reduction of nitrates, 424. 
relation of to other cycles, 410. 
Nitrogenous fertilizers, ammonium sul- 
fate, 449. 
calcium cyanimid, 451. 
calcium nitrate, 452. 
castor pomace, 446. 
cotton seed meal, 446. 
dried blood, 445. 
flsh scrap, 446. 
guano, 446. 
hoof meal, 446. 
leather meal, 446. 
linseed meal, 446. 
process goods, 446. 
relative availability, 454. 
sodium nitrate, 448. 
tankage, 445. 

utilized by higher plants, 411, 447. 
wool and hair waste, 446. 
Nitrosomonas in soils, 415. 
Nitrous acid, relation to mineral cycle, 

408. 
Nodules on the roots of leguminous plants, 

nature of, 434. 
Number of particles in soil, 96. 
Number of soil particles, calculation of, 

96. 
Nutrient elements used by plants, 
amounts in soil, 12. 
defined and explained, 8. 
listed, 9. 
primary, 10. 
source of, 10. 
Nutrients in soils, addition by leguminous 
green manures, 557. 
addition of in farm manure, 557. 
dift'erential diffusion into plants, 

293. 
difltusion into plants, 291. 



580 



INDEX OF SUBJECT MATTER 



Nutrients in soils, direct influence of 

plants on solubility of, 295. 
how lost from the soil, 289. 
influence of lime on solubility of, 

373. 
lost by drainage and cropping, 307. 
lost by leaching, Cornell data, 210. 
lost by plant influence, 303. 
lost during manurial production, 

cows, 516. 
lost during manurial production, 

heifers, 516. 
lost during manurial production, 

sheep, 516. 
lost during manurial production, 

steers, 516. 
lost from Cornell soil, 554. 
lost from soil, relative losses, 308. 
lost in handling and storage of ma- 
nure, 517. 
natural additions of to soil, 556. 
quantities removed by crops, data of, 

303. 
recovery of in farm manure, 616. 
solubility as influenced by carbon 

dioxide, 255. 
Nutrient losses from and addition to soil 

under various types of farming, 

558. 

Ocean, soils found in, 50. 

Ohio results with raw rock phosphate, 

462. 
Optimum soil moisture, influence of 
structure on, 201. 
for plant growth, 200. 
Organic carbon, determination of, 311. 

use of by higher plants, 402. 
Organic compounds of soil, character of, 
105. 
classification of, 107. 
nitrogenous, 106. 
relation to plants, 108. 
Organic decay, effect on soil tempera- 
ture, 239. 
Organic decomposition, simple products 

of, 110. 
Organic matter, amount in Nebraska 
loess, 120. 
amount in soil of United^tates, 117. 
decay of, 103. 
compounds isolated from, 108. 



Organic matter, defined, 99. 

determination of in soils, 112. 

effect of on soil acidity, 353. 

effect on capillary capacity of soil, 

164. 
effect on carbon dioxide of soil air, 

253. 
effect on specific heat, 233. 
influence in soil, 8. 
influence of soil conditions on decay 

of, 124. 
influence on availability of rock 

phosphate, 460. 
influence on the soil, 121. 
in Minnesota soils, 119. 
maintenance of in soil, 122. 
Organic matter of soil, effect on heat 
conductivity, 236. 
general nature, 7. 
influence on bacteria, 394. 
portion alive, 100. 
sources of, 7, 99. 
Organic nitrogenous compounds, utiliza- 
tion by higher plants, 411, 446. 
Organic nitrogenous fertilizers of secon- 
dary importance, 445. 
Organic toxins, elimination of, 109. 

of soil, 108. 
Organisms, benefits of in soil, 397. 

pounds of in soil, 384. 
Orthoclase, change of to koalinite, 26. 

importance in soil, 6. 
Osmosis, defined, 289. 

how demonstrated, 290. 
pressure developed by, 290. 
Osmosis of water into plants, 290. 
Osmotic pressure, nature of, 290. 
Oswald method of converting ammonia 

into nitric acid, 453. 
Outlets for tile drains, construction of, 

214. 
Oxidation, effect of on composition of soil 
air, 254. 
importance of in soil formation, 24. 
of sulfur in soil, 403. 
Oxidases, production of by plant roots, 

297. 
Oxygen, importance in soil air, 256. 

Packers, action of, 148. 
Partial analysis of soils, 315. 

digestion with dilute acids, 317. 



INDEX OF SUBJECT MATTER 



581 



Partial analysis of soils, digestion with 
dilute acids, objections, 318. 
digestion with dilute acids, value, 

318. 
digestion with strong acids, 316. 
digestion with strong acids, objec- 
tions, 316. 
extraction with water, 319. 
extraction with water, method of, 

321. 
extraction with water, value, 322. 
of Minnesota soils, 316. 
of Minnesota and Maryland soils, 
317. 
Partially decomposed matter of soils, 105. 
Particles of soil, number to a gram, 96. 
Peat, agricultural value of, 43. 
capillary capacity of, 164. 
character of, 43. 
chemical analj'sis of, 44. 
term defined, 43. 
Percolation, control of, 208. 
Cornell data, 209. 
efiects of crops on, 210. 
loss of nutrients by, 208. 
in arid regions, 208. 
in humid regions, 208. 
Rothamsted data, 207. 
Ph values of acidity explained, 350. 
Phosphate fertilizers, acid phosphate, 
456. 
basic slag, 457. 
bone phosphate, 454. 
relative availability of, 458. 
rock phosphate, 455. 
Phosphoric acid, amount of in acid phos- 
phate, 456. 
amount of in apatite, 6. 
amount of in basic slag, 457. 
amount of in igneous rocks, 6. 
amount of in manure, 501. 
amount of in bone, 454. 
amount of in rock phosphate, 455. 
amount of in soils, 12. 
forms of in fertilizers, 456. 
forms of in soil, 11. 
influence of green manures on, 545. 
influence of lime on reversion of, 

373. 
influence on plant growth, 474. 
in liquid and solid manure, 503. 
loss of from farm manure, 519. 



Phosphoric acid, loss of from soil, 555. 
losses from Cornell soils, 307. 
of food recovered in farm manure, 

516. 
of soil, 140. 

organic and inorganic in soils, 315. 
organic nature of, 11, 314. 
pounds removed by various crops, 

468. 
relative availability of in fertilizers, 
458. 
Phosphorus, see phosphoric acid. 
Physical absorption by soils, 263. 
Physiological character of plants in re- 
lation to alkali toxicity, 336. 
Piconometer, for determination of specific 

gravity, 90. 
Plankers, action of, 148. 
Plants, absorptive activity of as deter- 
mined by certain factors, 299. 
acquisition of nutrients by, 291. 
alkali vegetation, 340. 
capacity of to grow on poor soils, 

299. 
cause of drought resistance by, 195. 
cause of wilting, 194. 
detrimental influence of nitrogen on, 

473. 
differential diffusion into, 292. 
different absorptive capacity for soil 

nutrients, 301. 
direct influence of upon soil nu- 

nutrients, 296. 
effect of alkali on, 334. 
effect of calcium and magnesium 

ratio on, 376. 
effects of on percolation, 208. 
factors affecting transpiration from, 

188. 
function of water in, 184. 
growth of in acid medium, 350. 
influence of on the soil solution, 

284. 
influence of phosphorus on, 474. 
influence of potassium on, 475. 
influence of roots on soil colloids, 

297. 
influence of soil water on, 186. 
production of acids by, 296. 
productions of oxidases by, 297. 
reduction produced bj' roots of, 297. 
resistance of to alkali, 335. 



582 



INDEX OF SUBJECT MATTER 



Plants, response of to lime, 372. 

soil organisms injurious to, 396. 

tolerance of to soil acidity, 353. 

used for green manures, 546. 

utilization of ammonia by, 415, 450. 

utilization of organic carbon by, 402. 

utilization of organic nitrogen by, 
411, 447. 

water requirements of, 187. 
Plants and animals, relation to soil 

formation, 23. 
Plant diseases, control of in soil, 397. 
Plant food, defined, 8. 
Plant growth, factors for, 8. 

influence of nitrogen on, 472. 

optimum moisture for, 200. 

temperature for, 224. 
Plant nutrients, amounts in soil, 12. 

contained in minerals, 5. 

defined, 8. 

derived from air, 9. 

derived from soil, 9. 

listed, 9. 

primary, 10. 
Plant roots, production of carbon dioxide 
by, 252. 

prying effect on rocks, 23. 
Plant tissue, composition of, 100. 

method of analysis, 102. 
Plasmolysis, defined, 290. 
Plowing, influence of on the soil, 146. 
Pore space of soils, calculation of, 94, 
178. 

data on, 95. 

importance of, 95. 

nature of, 93. 
Potash, amount in soils, 12. 

fertilizers carrying, 463. 

forms of in soil, 11. 

ill farm manure, 501. 

influence on plant growth, 475. 

in liquid and solid manure, 503. 

in minerals, 6. 

loss of from soil, 555. 

loss of from farm manure, 519. 

losses from Cornell soils, 307. 

miscellaneous fertilizers of, 464. 

of food recovered in farm manure, 
516. 
Potash fertilizers, alunite, 465. 

feldspar, 465. 

flue dust, 465. 



Potash fertilizer, kelp, 465. 

lake salines, 465. 

leucite, 465. 

Stassfurt salts, 463. 

wood ashes, 464. 
Potassium, see potash. 
Potassium chloride as a fertilizer, 463. 
Potassium nitrate, use of in litmus test, 

358. 
Potassium sulfate as a fertilizer, 464. 
Poultry manure, character and composi- 
tion of, 503. 
Potatoes, influence of manure on, 534. 
Practical soil management, factors of, 

560. 
Precipitation, addition of sulfur by, 469. 
Pressure, effect on gravity water, 175. 

effect on movement of soil air, 260. 
Process fertilizers, nature of, 446. 
Productivity, as influenced by soil solu- 
tion, 287. 

equation of, 327. 
Protection, influence of on farm manure, 

525. 
Proteid compounds, changes of in de- 
caying manure, 510. 
Protozoa, importance of in soil, 387. 

number of in soil, 387. 

relation of to ammonification, 387. 

types of in soil, 387. 
Puddling of soils, 141. 
Purchase of commercial fertilizers, 483. 
Purchase of unmixed fertilizers, 484. 
Putrefaction, defined, 103, 410. 

of farm manure, 508. 

products of, 411. 

Qualitative composition of drainage 
water, 304. 
of the soil solution, 280. 
Quantitative composition of drainage 
water, 304. 
of soil solution, 282. 
Qualitative tests for soil acidity, 358. 

compared and criticized, 359. 
Quantitative tests for soil acidity, nature 
of, 355. 
value of, 357. 

Radiation, loss of heat from soil by, 240. 
Rain-water, analysis of, 429. 
sulfur in, 404. 



INDEX OF SUBJECT MATTER 



583 



Rational fertilizer practice, 497. 
Recovery of nutrients in fann manure, 

516. 
Reduction, as aflfected by plant roots, 

297. 
Reduction of nitrates in soil, 424. 
Reinforcement of farm manure, 527. 
agricultural value of, 529. 
balancing influence, 529. 
conserving effects, 529. 
Residual influence of manure, 531. 
Residual soils, age of, 39. 
analysis of, 33, 41. 
chemical composition of, 52, 57. 
compared with glacial soils, 57. 
colors of, 32, 39. 
formation of, 38. 
from specific rocks, 39. 
location of in U. S., 41. 
organic content, 41. 
Residues in soil from differential dif- 
fusion, 294. 
Resistance of plants to alkali, generalized 

table of, 338. 
Resistance to alkali by various plants, 

data on, 338. 
Reversion of mono-calcium phosphate in 

soil, 457. 
Reverted jjhosphoric acid, defined, 456. 
Rock phosphate, as a reinforcement for 
manure, 528. 
changes in soil, 456. 
compared with acid phosphate, 458. 
composition, 456. 
composted with manure, 462. 
influence of organic matter on, 460. 
Ohio results on, 462. 
source, 455. 

use of in sulfur composts, 406. 
Rocks, igneous, sedimentary and meta- 
morphic, 4. 
soil forming, 3. 
Rodents, macro, soil organisms, 384. 
Rollers, actions of, 148. 
Roots of higher plants, a type of macro- 
organism, 386. 
production of carbon dioxide by, 

295. 
production of exudates by, 296. 
Rooting habit of plants, in relation to 

alkali toxicity, 336. 
Rotation, farm manure and the, 532. 



Sampling of soil, method of, 311. 
Sand dunes, nature of, 64. 
Season, influence on soil solution, 283. 
Sedentary soil, explanation of term, 28. 
Sediment carried into ocean, 46. 
Selective absorption by soils, nature of, 
269. 
types of, 269. 
Selection of a commercial fertilizer, fac- 
tors to consider, 482. 
Sheet erosion and its control, 205. 
Size of colloidal particles, 128. 
Slope, influence on soil temperature, 229. 

influence upon absorption of solar 
insolation, 229. 
Sod, influence on nitrate accumulation, 

427. 
Sodium chloride as a soil amendment, 
380. 

presence of in alkali, 333. 
Sodium nitrate, changes in soil, 448. 

character of, 448. 

composition of, 448. 

retention of by soils, 321. 

origin of, 448. 

source of, 448. 
Soils, absorption by, 263. 

absorptive capacity of, 266. 

acid nature of, 345. 

acquisition of nitrogen by, 428. 

addition of sulfur to by precipita- 
tion, 469. 

aeolian, 61. 

alkali, 328. 

alluvial, 46. 

amendments used on, 363. 

ammonification in, 412. 

amounts of capillary water in, 166. 

amount of gravity water in, 177. 

available water of, 198. 

average composition of, 12. 

bulk analysis of, 311. 

capacity of to retain nitrates, 321. 

capillary capacity for water, 163. 

capillary movement of water in, 168. 

capillary water of, 159. 

cause of acid condition of, 351. 

changes of lime in, 369. 

cliemical analysis of water extract 
from, 320. 

coUuvial, 45. 
color of, 36. 



584 



INDEX OF SUBJECT MATTER 



Soils, composition of air in, 247. 

conductivity coefficients of, 236. 
conditions, effect on nitrification, 

418. 
control of air in, 261. 
control of alkali in, 343. 
control of erosion, 205. 
cumulose, 42. 
defined, 2. 

diseases, control of, 397. 
diseases, nature of, 396. 
dynamic nature of, 3. 
eradication of alkali from, 341. 
erosion of by water, 204. 
fertility evaluation of by chemical 

analysis, 323. 
formation of, 16. 
forms of water in, 152. 
functions of water in, 184. 
general composition of, 2. 
geological classification of, 38. 
glacial, 54. 

granulation of, defined, 139. 
handling of alkali soils, 340. 
heat conduction in, 234. 
heat convection in, 238. 
hygroscopic water of, 152. 
importance of absorption by, 273. 
influence of earth worms on, 385. 
insolation received by, 225. 
lacustrine, 58. 
losses of water from, 202. 
management, practical factors of, 

560. 
marine, 50. 
metliod of moisture determination 

on, 161. 
moisture data of, 200. 
movement of air in, 258. 
movement of gravity water in, 175. 
mulch on, 218. 
names in common use, 82. 
names, origin and meaning, 80. 
nitrification in, 416. 
nitrogen content of, 118. 
partial analysis of, 315. 
partial analysis with strong acids, 

316. 
partial analysis with weak acids, 

317. 
particles of, 67. 
plasticity of, 140. 



Soils, pore space of, 93. 

practical management of, 560. 

productivity of as related to soil 
solution, 287. 

puddling of, 141. 

reaction, importance of, 345. 

reaction, types of, 345. 

reduction of nitrates in, 424. 

residual, 38. 

sampling of, 311. 

series defined, 86. 

specific gravity of, 88. 

specific heat data, 232. 

sulfofying power of, 405. 

survey classification of, 85. 

tests for acidity in, 354. 

thermal movement of moisture in, 
182. 

the solution of, 275. 

tilth, defined, 149. 

toxins of organic nature, 108. 

type defined. 86. 

weathering, importance of, 37. 

weight of, data, 93. 

wilting coefficient, 197. 
Soil acidity, active toxic bases, 346. 

as influenced by absorption, 274. 

causes of development, 352. 

causes of harmful effects, 346. 

expression of by ph values, 350. 

general nature of, 345. 

influence of absorption on, 352. 

influence of fertilizers on, 353. 

influence of leaching on, 352. 

influence on bacteria, 395. 

influence on nitrification, 421. 

lack of calcium in relation to, 348. 

lack of nutrients tlieory, 348. 

lime requirements, determination of, 
355. 

litmus paper test for, 358. 

present status of question, 349. 

relation of iron to, 347. 

relation of manganese to, 347. 

resume of, 360. 

tests for, 354. 

theory, aluminum, 347. 

theory, hydrogen ion, 346. 

tolerance of plants to, 353. 

Truog test for, 358. 

types of tests, 355. 

zinc sulfide test for, 358. 



INDEX OF SUBJECT MATTER 



585 



Soil air, carbon dioxide of, 250. 

general characteristics, 247. 

composition data, 248, 250. 

control of, 261. 

general composition of, 247. 

movement of, 258. 

resume of, 262. 

types of, 249. 

volume of, 257. 
Soil amendments, forms of lime, 363. 

organic matter important as, 124. 
Soil analysis, alluvial and upland, 49. 

arid and humid soils, 31. 

determination of organic matter, 
112. 

glacial soils, 57. 

granite soil, 33. 

good and poor soils, 326. 

humus determination of, 115. 

humus in California soils, 120. 

humus in Nebraska soils, 120. 

lime requirement of soil, 355. 

limestone soil, 33. 

loess soils, 63. 

marine soils, 52. 

mechanical, 67. 

nitrogen in California soils, 120. 

nitrogen in Nebraska soils, 120. 

nitrogen in soils of United States, 
118. 

organic matter in Nebraska loess, 
120. 

organic matter in Minnesota soils, 
119. 

organic matter in soils of United 
States, 117. 

peat and muck, 44. 

residual soils, 41, 52, 57. 
Soil class, discussion of, 79. 

determination from a mechanical 
analysis, 84. 

practical determination of, 83. 
Soil colloids, absorption by, 265. 

as influenced by plant roots, 297. 

generation of, 132. 

importance of, 135. 

influence of, 135. 

resume of, 138. 
Soil color, cause of, 36. 

significance of, 36. 
Soil erosion and its control, 204. 

types of, 205. 



Soil exhaustion, discussion of, 309. 

possibility of, 3 OS. 

time for, 309. 
Soil extraction, a metliod of studying the 

soil solution, 279. 
Soil fertility, defined, 554. 

effect on transpiration, 192. 

factors involved in maintenance, 554. 

importance of nitrification to, 423. 

influence of plants and animals on, 
23. 

maintenance program of, 560. 

relation of sulfur to, 468. 

sources of knowledge, 554. 
Soil formation, forces of, 16. 

general statement of, 29. 

glacial action, 18. 

influence of carbonation, 26. 

influence of climate, 30. 

influence of hydration, 26. 

influence of solution, 27. 

oxidation and deoxidation, 24. 

processes classified, 16. 

special cases of, 32. 

temperature changes, 21. 

water action, 17, 19. 
Soil heat, importance of, 223. 

influence of on the soil, 224. 

loss of by conduction, 240. 

loss of by evaporation, 240. 

loss of by radiation, 240. 

transfer of, 238. 
Soil humus, determination of, 115. 
Soil minerals, importance of, 6. 

list of, 5. 
Soil moisture, conservation of, 219. 

data of, 179. 

effect on conductivity of heat, 236. 

effect on heat capacity, 233. 

effect on transpiration, 191. 

importance of amount in plowing, 
146. 

influence of on the soil solution, 
286. 

optimum for efficient tillage, 150. 

optimum for plants, 200. 

relation of to granulation, 142. 
Soil mulcli and moisture conservation, 
221. 

relation of to capillary movement, 
175. 

use of, 218. 



586 



INDEX OF SUBJECT MATTER 



Soil organic matter, amount of in 

Minnesota soils, 119. 
amount of in soils of United States, 

117. 
general nature, 7. 
importance of, 121. 
maintenance of, 122. 
resume of, 126. 
source and character of, 99. 
Soil organisms, and the free-fixation of 

nitrogen, 431. 
benefits of, 397. 
general methods of study, 399. 
groups of, 384. 

influence in nitrate assimilation, 426. 
influence of alkali on, 335. 
injurious to higher plants, 396. 
macro-animal forms, 384. 
macro-plant forms, 385. 
micro-animal forms, 386. 
micro-plant forms, 388. 
resume of, 440. 
Soil particles, character as determined by 

size, 69. 
classification of, 67. 
minerological character, 75. 
number of, 95. 
surface of, 97. 
Soil separates, chemical and minerological 

characters, 75. 
chemical composition of, 78, 79. 
physical characters of, 73. 
sizes of, 67. 
specific gravity of, 89. 
Soil solution, as studied by aqueous ex- 
traction, 279. 
as studied by depression of freezing 

point, 280. 
composition data of, 283, 288. 
concentration data of, 282, 285, 

286. 
general character of, 275. 
influence of crop on, 284. 
influence of miscellaneous factors on 

286. 
influence of season on, 283. 
methods of study, 277. 
qualitative composition of, 280. 
quantitative composition of, 282. 
relation to absorption, 276. 
relation to productivity, 287. 
summary of, 288. 



Soil structure, ideal, 88. 

nature of, 87. 

types of, 139. 
Soil temperature, control of, 244. 

data of, 243. 

influence of slope, 229. 

variations of, 242. 
Soil water, availability of, 198. 

diagram of forms, 199. 

effect on air movement, 258. 

effect on specific heat of soils, 233. 

form of molecule, 28. 

forms of, 151. 

function to plants, 184. 

general characteristics of, 152. 

influence on plants, 18G. 

loss by evaporation, 216 

loss by percolation, 206. 

loss by percolation at Cornell, 209. 

loss by percolation at Rothamsted, 
207. 

modes of loss, 202. 

methods of expressing, 156 

run-off losses, 203. 

summary of control, 221. 

thermal movement of, 182. 
Soluble matter carried into ocean, 40. 
Soluble salts in soil, influence on nitri- 
fication, 421. 
Solubility of nutrients as influenced by 

carbon dioxide, 255. 
Solution, loss of nutrients because of, 2S. 

importance of in soil formation, 27. 

relation of to soil productivity, 28. 
Specific gravity of minerals, 89. 
Specific gravity of soils, defined, 88. 

determination of, 90. 
Specific gravity of soil separates, 89. 
Specific heat, data on soils, 232. 

defined, 231. 
Specific heat of soil, 231. 

factors affecting, 232. 
Stages ill the decay of green manures, 

542. 
Stassfurt salts, chlorides and sulfates, 
463. 

kainit, 463. 

silvinit, 463. 
Stone drains, construction of, 212. 
Straw, influence on nitrate reduction, 

425. 
Streams, soil formation by, 46. 



INDEX OF SUBJECT MATTER 



587 



structure of soil, effect on capillary 
capacity, 164. 

effect on capillary movement, 174. 

effect on gravity water, 176. 

effect on heat conductivity, 236. 

ideal condition, 88. 

influence on optimum water, 201. 

nature of, 87. 

summary of, 149. 

types of, 139. 
Substitutions of bases in soils, 270. 
Sulfate sulfur as a fertilizer, 468. 
Sulfofication, effect of lime on, 405. 

factors influencing, 405. 

influence on carbon dioxide produc- 
tion, 255. 

determination of, 405. 

reactions of, 403. 

relation of to mineral cycle, 408. 
Sulfur, amount added to soil in precipi- 
tation, 469. 

amount in soils, 13. 

as a fertilizer, 467. 

experiments with as a fertilizer, 
467. 

forms of in soil, 11. 

how lost from soil, 404. 

importance of in soil fertility, 470. 

loss of from Cornell soils, 307, 404. 

loss of from soil, 5.35. 

natural addition to soil, 557. 

oxidation of in soils, 403. 

possible deficiency in arable soils, 
468. 

pounds removed by various crops, 
468. 

sources of in soils, 403. 

use in composting, 406. 

use of as a sulfate, 468. 
Sulfur composts, 406. 
Sulfur cycle of soil, losses of sulfur from, 
404. 

sources of sulfur, 403. 

sulfofication, 403. 
Sulfurous acid, relation to mineral cycle, 

408. 
Superfluous water, 198. 
Surface of soil particles, calculation of, 
97. 

importance of, 97. 
Surface tension, defined, 160. 

effect on capillarity, 170. 



Surface tension, force of, 160. 

relation to capillary movement, 169. 
Synergism, relation of to plant absorp- 
tion, 300. 

relation of to soil acidity, 349. 

nature of, 349. 
Systems of applying fertilizers, 496. 

Tankage changes in soil, 445. 

character of, 445. 

composition of, 445. 

source of, 445. 
Temperature of soil, control of, 244. 

data of, 243. 

effect of change on soil air, 259. 

effect on capillary capacity, 163. 

effect on gravity water, 176. 

importance in soil formation, 21. 

influence of decay on, 239. 

influence of slope, 230. 

Influence on bacteria, 394. 

influence on hygroscopic coefliclent, 
158. 

influence on nitrification, 420. 

variations of, 242. 
Temperatures for crop growth, 224. 

for germination of seeds, 224. 
Terracing, 205. 
Texture of soil, definition of, 66. 

effect on absorption, 267. 

effect on capillary capacity, 164. 

effect on capillary movement, 173. 

effect on gravity water, 176. 

effect on heat conduction, 236. 

effect on specific heat, 232. 

influence on moisture equivalent, 
168. 
Thermal movement of soil water, na- 
ture of, 182. 

relation to evaporation, 182. 
Tile drains, depth and interval of, 214. 

effective grade for, 214. 

functions of, 212. 

outlets of, 214. 

size of tile, 213. 

study of drainage water from, 180. 

systems, 212. 

table for determination of size, 214. 
Tillage, influence on granulation, 144. 

influence on soil solution, 286. 

killing of weeds by, 219. 
Tilth of the soil, defined, 149. 



588 



INDEX OF SUBJECT MATTER 



Time, influence on absorption by soils, 
269. 

Time of applying fertilizers, 495. 

Tolerance of plants to soil acidity, 353. 

Tramping, influence on farm manure, 
524. 

Transpiration, factors affecting, 188. 

Transpiration ratio, defined, 187. 
determination of, 187. 
of different crops, data, 189. 

Transported soil, explanation of term, 28. 

Truog test for soil acidity, 358. 

Types of farming, influence on the main- 
tenance of fertility, 558. 

Urea, ammonification of, 414. 

decomposition of in manure, 509. 
production of from calcium cyana- 
mid, 250. 
Unavailable water in soil, 198. 
Unmixed fertilizers, purchase of, 484. 

use of, 484. 
Utilization of ammonium in salts by 
higher plants, 450. 
of organic compounds by plants, 
446. 

Variability of farm manure, 506. 
Value of farm manure, agricultural, 513. 

commercial, 512. 
Vegetables, fertilizer formulae for, 491. 
Vegetation, resistant to alkali, 340. 
Veitch method of determining the lime 
requirement of soils, 356. 

procedure, 356. 

value of, 357. 
Viscosity, effect on capillarity, 170. 
Volcanic dust, as soil, 65. 
Volume of soil air, 257. 

calculation of, 258. 
Volume weight, determination of, 91. 

relation to specific gravity, 94. 
Volume weight of soils, data, 93. 

explanation of, 91. 
Water, alkali in river water, 332. 

availability of to plants, 198. 

deposition of sediment by, 46. 

diagrams of forms in soil, 199. 

effect on rocks by freezing, 23. 

erosive effects of, 204. 

function of to plants, 184. 

in farm manure, 501. 



Water, influence on concentration of soil 
solution, 286. 
influence on plants, 186. 
intake of by plants, 289. 
loss of from soil, 202. 
loss of from soil by percolation, 

206. 
loss of from soil by evaporation, 

216. 
mechanical action of, 17. 
methods of expression in soil, 156. 
movement in soil, 168, 175, 182. 
movement in soil in relation to 

plants, 193. 
production of hydration by in soil, 

27. 
relation of to granulation, 142. 
required to mature a crop, 193. 
use of alkali water in irrigation, 
333. 
Water requirements of plants, factors 
affecting, 188. 
investigations of, 189. 
nature of, 187. 
Water slaked lime, 364. 
Water soluble phosphoric acid, defined, 

456. 
Weathering, character of in arid regions, 
30. 
character of in humid regions, 30. 
defined, 16. 
losses due to, 33. 
of granite, 33. 
of limestone, 33. 
of soil, practical relations of, 37. 
relation of to alkali, 331. 
Weeds, killing of, 219. 
Weight of soils, data of, 93. 
Wilting, cause of, 194. 

explanation of, 194. 
Wilting coefiicient, calculation of, 198. 
determination of, 196. 
effect of texture on, 196. 
explained, 195. 
for different soils, 197. 
Wind in soil formation, 19. 
Wool and hair waste, composition of, 
446. 

Zinc-Bulfide test, criticism of, 360. 

for soil acidity, 358. 
Zeolites, not present in soil, 265. 




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